feat: rds information in the integration secret

[jakeyheath]

It would be great if the RDS information such as the host, username, and password were in the integration secret. These all need to be consumed by the application code to connect to the database so it makes sense that they would live there. I can contribute this change, just documenting the use case here because as of right now, I had to go to the statefile to see the RDS password and manually copy it into my parameter store.