Support FileSourceRelation to load CSV in PPL

[LantaoJin]

Description

This PR is for the syntax option B described in #638
The PR for option A is #678.

Syntax of option B

search file=<tempTableName> <fileUrl> [predicate]

Usage:

search file=table1 "s3://bucket_name/folder1/folder2/flights.csv" FlightDelay > 500
search file=table1 "s3://bucket_name/folder1/folder2/flights.csv.gz" FlightDelay > 500
search file=table1 "s3a://bucket_name/folder1/folder2/flights.parquet" FlightDelay > 500

Only single file is supported now.

PS: the current search command syntax is

search index=<indexName> [predicate]
search source=<indexName> [predicate]

Issues Resolved

Resolves #638

Check List

• Updated documentation (ppl-spark-integration/README.md)
• Implemented unit tests
• Implemented tests for combination with other commands
• Commits are signed per the DCO using --signoff

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[YANG-DB]

@LantaoJin I would go with option A as shown in #678
Thanks again for u'r support and contributions

[YANG-DB]

@LantaoJin can u resolve the latest conflict plz ?

[YANG-DB]

@LantaoJin can u plz change to PR into draft mode ?