[Feature] Add lower case with snake case for field names and table names in PostgreSQL's inbox and outbox.

[aidanlim90]

The current table and field names in PostgreSQL's inbox and outbox are in lowercase without snake case. May I request the addition of an option to enable lowercase with snake case for field and table names for inbox and outbox in Postgres.

Example
firstname => first_name

[iancooper]

@aidanlim90 Let me take a look, this will probably be post v10 as we have a number of changes to how we handle the RDBMS support there