Python RDS and Aurora MVPs

[Laren-AWS]

This PR completes work for several issues:

• Python RDS MVP #3405

  • [x] Code for actions and scenarios
  • [x] Unit and integration tests
  • [x] SOS metadata
  • [x] README

• Python Aurora MVP #3612

  • [x] Code for actions and scenarios
  • [x] Unit and integration tests
  • [x] SOS metadata
  • [x] README

• SOS feature indirection #3600

Happily this required no code changes and was accomplished simply by treating Aurora as a service in the SOS YAML, which causes the system to output a separate Aurora code examples chapter, etc., which is what we want.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.