[Feature Request] Add MERGE command support to the PostgreSQL JDBC sink module

[h6ah4i]

WHAT

Adding the INSERT_OR_UPDATE mode support for PostgreSQL JDBC sink.

WHY

Currently, the INSERT_OR_UPDATE mode is only available for MySQL.

Recent versions of PostgreSQL (v15+) support MERGE SQL command that can be used to achieve the INSERT_OR_UPDATE behavior.

ref.) https://www.postgresql.org/docs/current/sql-merge.html