remove opensearch.sql.engine.new.enabled setting

[penghuo]

Signed-off-by: penghuo penghuo@gmail.com

Description

Remove the opensearch.sql.engine.new.enabled. The opensearch.sql.engine.new.enabled setting is added and set to default true on ODFE 1.13.0.0, the major purpose is to safely publish the new engine, in any case, the customer found issue, they still have the way to rollback to the legacy engine.
We didn't found major issue with new engine, so we decide to fullly enable it by default. If there are any case the new engine can't handle, it still fallback to the the legacy engine automatically. So, there is no impact for the customer.

Issues Resolved

#58

To Reviewers

The PR include the following changes

1. Change the SQL entry point logic, the new engine is default now.
2. Remove the integration test against the legacy engine.
3. Ignore some IT which only work for legacy engine.
4. Remove the opensearch.sql.engine.new.enabled related docs accordingly.

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[chloe-zh]

Here is another doc that needs to be updated: https://github.com/opensearch-project/sql/blob/main/docs/dev/NewSQLEngine.md#34-what-if-something-wrong

[penghuo]

Here is another doc that needs to be updated: https://github.com/opensearch-project/sql/blob/main/docs/dev/NewSQLEngine.md#34-what-if-something-wrong

Done. https://github.com/penghuo/os-sql/blob/pr-issue58/docs/dev/NewSQLEngine.md

[dai-chen]

LGTM!