Canvas needs to handle arrays in elasticsearch raw documents better

[bhavyarm]

Kibana version: 7.6.0 BC2

Elasticsearch version: 7.6.0 BC2

Server OS version: darwin_x86_64

Browser version: chrome latest

Browser OS version: OS X

Original install method (e.g. download page, yum, from source, etc.): from staging

Describe the bug: If your elasticsearch raw document data source contains arrays - Canvas displays - " Whoops! Expression failed
Expression failed with the message:
[esdocs] > Unexpected error from Elasticsearch: [sql_illegal_argument_exception] Arrays (returned by [@tags]) are not supported"

This is not very helpful to novice user as the datasource is es raw documents and there is no obvious involvement of SQL here as user won't know that canvas uses sql to talk to es at the backend.

Steps to reproduce:

1. Download & load logstash data to ES from build your own dashboard tutorial from docs - https://www.elastic.co/guide/en/kibana/current/tutorial-build-dashboard.html#tutorial-load-dataset and create logstash index pattern
2. Start Kibana and ES and open Canvas app and start a new workpad
3. Add an area chart element and change the data source to elasticsearch raw documents and pick logstash indexpattern
4. Kibana displays '[esdocs] > Unexpected error from Elasticsearch: [sql_illegal_argument_exception] Arrays (returned by [@tags]) are not supported'

Expected behavior: Kibana needs to handle the datasets with arrays better. or display more helpful error message

Screenshots (if relevant):

Provide logs and/or server output (if relevant): ES logs:

[2020-01-28T15:22:02,703][WARN ][r.suppressed             ] [Bhavyas-MBP.localdomain] path: /_sql, params: {format=json}
org.elasticsearch.xpack.sql.SqlIllegalArgumentException: Arrays (returned by [@tags]) are not supported
	at org.elasticsearch.xpack.sql.execution.search.extractor.FieldHitExtractor.unwrapMultiValue(FieldHitExtractor.java:173) ~[?:?]
	at org.elasticsearch.xpack.sql.execution.search.extractor.FieldHitExtractor.extractFromSource(FieldHitExtractor.java:288) ~[?:?]
	at org.elasticsearch.xpack.sql.execution.search.extractor.FieldHitExtractor.extract(FieldHitExtractor.java:153) ~[?:?]
	at org.elasticsearch.xpack.sql.execution.search.SearchHitRowSet.extractValue(SearchHitRowSet.java:128) ~[?:?]
	at org.elasticsearch.xpack.sql.execution.search.SearchHitRowSet.extractValue(SearchHitRowSet.java:31) ~[?:?]
	at org.elasticsearch.xpack.sql.execution.search.ResultRowSet.getColumn(ResultRowSet.java:37) ~[?:?]
	at org.elasticsearch.xpack.sql.session.AbstractRowSet.column(AbstractRowSet.java:18) ~[?:?]
	at org.elasticsearch.xpack.sql.session.RowView.forEachColumn(RowView.java:38) ~[?:?]
	at org.elasticsearch.xpack.sql.plugin.TransportSqlQueryAction.lambda$createResponse$2(TransportSqlQueryAction.java:111) ~[?:?]
	at org.elasticsearch.xpack.sql.session.RowSet.forEachRow(RowSet.java:27) ~[?:?]
	at org.elasticsearch.xpack.sql.plugin.TransportSqlQueryAction.createResponse(TransportSqlQueryAction.java:109) ~[?:?]
	at org.elasticsearch.xpack.sql.plugin.TransportSqlQueryAction.createResponseWithSchema(TransportSqlQueryAction.java:104) ~[?:?]
	at org.elasticsearch.xpack.sql.plugin.TransportSqlQueryAction.lambda$operation$0(TransportSqlQueryAction.java:80) ~[?:?]
	at org.elasticsearch.action.ActionListener$1.onResponse(ActionListener.java:63) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.ActionListener$1.onResponse(ActionListener.java:63) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.ActionListener$1.onResponse(ActionListener.java:63) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.xpack.sql.execution.search.Querier$ScrollActionListener.lambda$handleResponse$1(Querier.java:486) [x-pack-sql-7.6.0.jar:7.6.0]
	at org.elasticsearch.xpack.sql.execution.search.ScrollCursor.handle(ScrollCursor.java:130) [x-pack-sql-7.6.0.jar:7.6.0]
	at org.elasticsearch.xpack.sql.execution.search.Querier$ScrollActionListener.handleResponse(Querier.java:485) [x-pack-sql-7.6.0.jar:7.6.0]
	at org.elasticsearch.xpack.sql.execution.search.Querier$BaseActionListener.onResponse(Querier.java:558) [x-pack-sql-7.6.0.jar:7.6.0]
	at org.elasticsearch.xpack.sql.execution.search.Querier$BaseActionListener.onResponse(Querier.java:532) [x-pack-sql-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.support.TransportAction$1.onResponse(TransportAction.java:70) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.support.TransportAction$1.onResponse(TransportAction.java:64) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.search.AbstractSearchAsyncAction.sendSearchResponse(AbstractSearchAsyncAction.java:539) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.search.ExpandSearchPhase.run(ExpandSearchPhase.java:117) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.search.AbstractSearchAsyncAction.executePhase(AbstractSearchAsyncAction.java:347) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.search.AbstractSearchAsyncAction.executeNextPhase(AbstractSearchAsyncAction.java:341) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.search.FetchSearchPhase.moveToNextPhase(FetchSearchPhase.java:216) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.search.FetchSearchPhase.lambda$innerRun$1(FetchSearchPhase.java:105) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.search.CountedCollector.countDown(CountedCollector.java:53) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.search.CountedCollector.onResult(CountedCollector.java:64) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.search.FetchSearchPhase$2.innerOnResponse(FetchSearchPhase.java:172) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.search.FetchSearchPhase$2.innerOnResponse(FetchSearchPhase.java:167) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.search.SearchActionListener.onResponse(SearchActionListener.java:45) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.search.SearchActionListener.onResponse(SearchActionListener.java:29) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.ActionListenerResponseHandler.handleResponse(ActionListenerResponseHandler.java:54) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.search.SearchTransportService$ConnectionCountingHandler.handleResponse(SearchTransportService.java:414) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.transport.TransportService$ContextRestoreResponseHandler.handleResponse(TransportService.java:1108) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.transport.TransportService$DirectResponseChannel.processResponse(TransportService.java:1186) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.transport.TransportService$DirectResponseChannel.sendResponse(TransportService.java:1166) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.transport.TaskTransportChannel.sendResponse(TaskTransportChannel.java:54) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.support.ChannelActionListener.onResponse(ChannelActionListener.java:47) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.support.ChannelActionListener.onResponse(ChannelActionListener.java:30) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.ActionRunnable.lambda$supply$0(ActionRunnable.java:58) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.action.ActionRunnable$2.doRun(ActionRunnable.java:73) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:37) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.common.util.concurrent.TimedRunnable.doRun(TimedRunnable.java:44) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:692) [elasticsearch-7.6.0.jar:7.6.0]
	at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:37) [elasticsearch-7.6.0.jar:7.6.0]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) [?:?]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) [?:?]

[elasticmachine]

Pinging @elastic/kibana-canvas (Team:Canvas)