[CT-3090] Support properties for null value coalescing in metrics

[QMalcolm]

Details

It was raised in MetricFlow recently that null values aren't always handled gracefully (dbt-labs/metricflow#764). The proposed solution (dbt-labs/metricflow#759) requires some changes to the Metric sub protocols as define in the dbt-semantic-interfaces issue (dbt-labs/dbt-semantic-interfaces#142). Once the changes have been made in dbt-semantic-interfaces, we'll want to update our implementation of the affected protocol and the associated parsing logic (unparsed definition, schema_yaml_reader)

Acceptance Criteria

• People can specify join_to_timespine boolean value in their metric type params measure inputs
  • If not specified, default to False
• People can specify fill_nulls_with integer value in their metric type params measure inputs
  • If not specified, default to None
• join_to_timespine and fill_nulls_with are propagated to semantic_manifest.json

Blocked By

dbt-labs/dbt-semantic-interfaces#142

Backport

The issue in DSI will be backported to DSI 0.2.latest and that will allow for backporting to dbt-core 1.6.latest.