Add Join operator support for Generic JDBC platform

[mohit-devlogs]

This PR adds support for the Join operator in the Generic JDBC platform.

Changes

• Introduced GenericJdbcJoinOperator for the enhancement of the functionality of the Join operator.
• Introduced JoinMapping for the enhancement of the logical JoinOperator for the execution operator of the Generic JDBC platform.
• Introduced SQL JOIN pushdown for the Generic JDBC platform, if possible.

Notes

• Depending upon the JDBC platform, for example, Postgres.
• Manages generic JoinOperator by casting if required.
• Successfully compiled with mvn clean install.

[mohit-devlogs]

Hi,

This PR duplicates my earlier work on the same feature. To avoid splitting the review discussion, I’ll consolidate all updates into the original PR and continue there.

Thanks!