Add information how to run Debezium + RDS Postgres

Improving on information documented in this issue: DBZ-3197

To be able to run Debezium without elevated permission you have to create the publication first:

CREATE PUBLICATION dbz_publication FOR ALL TABLES; 

Other information described in DBZ-3197 is still valid.

The steps that I followed:

1) Create a new database, create "my_role"

2) Create schema, ensure the owner of the schema, table, etc. is "my_role"

3) Create replication user add it to "my_role" (this replication user now have SELECT permission to the schema)

4) Grant rds_replication to the replication user

5) Create the publication

6) Debezium is now running without using master user or rds_superuser rights. Happy days.