Enable push down optimization by default

[qianheng-aws]

Description

In the previous implementation, we push down project/filter into OpenSearchProjectIndexScanRule without any updating on its digest, which uniquely identifies a RelNode. This causes an equivalent issue with the nodes of CalciteOpenSearchIndexScan and makes the different RelSets in the optimizer mess up inaccurately.

This PR fixes this issue by overriding the explainTerms method to reflect PushDownContext in its final computed digest. And enable the push down by default in our settings, since all tests work fine the feature.

./gradlew :integ-test:integTest --tests '*Calcite*IT' succeed locally.

Check List

• New functionality includes testing.
• New functionality has been documented.
• New functionality has javadoc added.
• New functionality has a user manual doc added.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

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[LantaoJin]

CalcitePPLJoinIT. testComplexAntiJoin
CalcitePPLJoinIT. testComplexCrossJoin
CalcitePPLJoinIT. testComplexInnerJoin
CalcitePPLJoinIT. testComplexLeftJoin
CalcitePPLJoinIT. testComplexRightJoin
CalcitePPLJoinIT. testComplexSemiJoin
CalcitePPLJoinIT. testJoinTwoColumnsAndDisjointFilters
CalcitePPLJoinIT. testJoinWithCondition
CalcitePPLJoinIT. testJoinWithTwoJoinConditions
CalcitePPLJoinIT. testNonEquiJoin

These ITs failed after merged this PR.
Some IT failed with Caused by: OpenSearchStatusException[OpenSearch exception [type=parsing_exception, reason=[terms] unknown token [END_ARRAY] after [country]]]
And others IT failed with different output ordering (may not a problem if we accept the the result without ordering) @qianheng-aws

[qianheng-aws]

CalcitePPLJoinIT. testComplexAntiJoin
CalcitePPLJoinIT. testComplexCrossJoin
CalcitePPLJoinIT. testComplexInnerJoin
CalcitePPLJoinIT. testComplexLeftJoin
CalcitePPLJoinIT. testComplexRightJoin
CalcitePPLJoinIT. testComplexSemiJoin
CalcitePPLJoinIT. testJoinTwoColumnsAndDisjointFilters
CalcitePPLJoinIT. testJoinWithCondition
CalcitePPLJoinIT. testJoinWithTwoJoinConditions
CalcitePPLJoinIT. testNonEquiJoin

These ITs failed after merged this PR. Some IT failed with Caused by: OpenSearchStatusException[OpenSearch exception [type=parsing_exception, reason=[terms] unknown token [END_ARRAY] after [country]]] And others IT failed with different output ordering (may not a problem if we accept the the result without ordering) @qianheng-aws

Seems PredicateAnalyzer has problem on support expression OR. Create a new issue to track this here #3368