AWS: RDS Postgres Read Replica

[BSick7]

Summary

Add a new module for creating RDS postgres read replicas.

How will it work?

This module will require a connection to a rds postgres datastore. All configuration will be pulled from that datastore to create another postgres instance that is configured as a read replica of the primary instance.

Caveats

Nullstone does not currently support multiple capabilities of the same type. As a result, a single service will be unable to connect to a primary and read replica.