Update and restructure MySQL integration docs

[alistairmatthews]

The existing MySQL integration document is comprehensive but difficult for beginners. This PR is intended to keep the comprehensive information but make it easier for those who want to get going quickly. I've used Copilot to propagate changes from the new PostgreSQL documents to the MySQL ones.

This PR:

• Splits the large integration doc into two: Hosting and Client.
• Adds a getting started short tutorial.
• Adds a getting started tutorial for both hosting and client integration.
• Adds a Properties of the PostgreSQL resources section to the client reference docs. This describes what configuration values are injected by the WithReference() method.

[alistairmatthews]

Just want to do some more code testing before this is ready for review.