Enable amplify to access RDS instances

**Is your feature request related to a problem? Please describe.**
I've been using amplify for a few weeks and it appears to be lacking this basic functionality; you simply cant connect it to a traditional RDS instance like SQL Server or PSQL.

**Describe the solution you'd like**
Ideally you would be able to deploy your next app with an ORM and database of your choice connecting to a given RDS instance.

**Describe alternatives you've considered**
Checking just about every article on the web on the topic.

- The GraphQL / app sync method does not work for the instances that im interested in (MySQL, PSQL)
- Opening the RDS instance to the web is not security compliant