PostgreSQL connector should work on Amazon RDS and be able to use the available plugin

PostgreSQL on Amazon RDS does not allow custom plugins, which means Debezium's PostgreSQL connector can't work with RDS since the connector requires installation of the Debezium decoderbufs plugin.

However, PostgreSQL on Amazon RDS does have installed the PostgreSQL 'test_decoding' output plugin that can be used to capture changes.

The Debezium PostgreSQL connector should transparently support using either this `test_decoding` plugin or Debezium's decoderbufs plugin.