Read replica support
Created by: josedcs
Added support for a master db with a read replica. Need to add the following environment variables for the configuration of the read replica to EB Configuration before deployment.
RDS_REPLICA_NAME RDS_REPLICA_HOST RDS_REPLICA_USERNAME RDS_REPLICA_PASSWORD
wp-settings.php automatically uses db.php if present.
With this configuration it works with two db instances one is the master the other is the read replica. We can add more instances in wordpress/db-config.php.