Add support for Managed MySQL advanced config

[christhemorse]

Description

This PR adds support for Managed MySQL advanced configuration options using the existing endpoint that previously was exclusive to PostgreSQL. It functions exactly the same and the validation takes care of the distinction between the two database engine types.

Checklist:

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you linted your code locally prior to submission?
• Have you successfully ran tests with your changes locally?

[optik-aper]

Looks good