Prototype adding an RDS data store in NextJS prototype

As a way to decide on #39, prototype adding a Cloud.gov-brokered RDS data store to the existing NextJS prototype.

This database prototype should include:

• how to exchange database credentials properly for dev and prod-like environments
• how to fetch data
• how to update data
• how to run database migrations

The purpose of this prototype is more to validate the operations around the database, rather than deciding on the data schema itself. Therefore, data schema should be kept very basic (i.e. "hello database").

CG pages team has a version of this implementation, although it was suggested that we avoid their specific architecture.

Acceptance criteria

Prototype validates each of the above items