chore: Update RDS instance type

[LeonLuttenberger]

Describe your changes

I'm updating the instance type for the MySQL DB after getting this message from AWS:

Starting March 11, 2024, Amazon RDS will begin disabling the creation of Amazon RDS for MySQL, MariaDB, and PostgreSQL database instances running on M4, R4, or T2 instance types.

Checklist before requesting a review

• I updated CHANGELOG.MD with a description of my changes
• If the change was to a module, I ran the code validation script (scripts/validate.sh)
• If the change was to a module, I have added thorough tests
• If the change was to a module, I have added/updated the module's README.md
• If a module was added, I added a reference to the module to the repository's README.md
• I verified that my code deploys successfully using seedfarmer apply

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

[kukushking]

thanks