Update database documentation with first generated parts

Closes #1302 (closed)

What does this MR do?

Update database documentation and provides a generator to extract the information directly from the database. Additionally, the generator provides information about the usage of the database tables by the PHP modules (like gateways).

How confident are you it won't break things if deployed?

No code change, only documentation. It changes the mdbook docker image, so it may break the dev doc generator on deployment.

How to test

1. Read the documentation
2. Check the pages of the dev doc

Checklist

• asked someone for a code review
• set a "for:" label to indicate who will be affected by this change
• added to the next milestone (see https://gitlab.com/foodsharing-dev/foodsharing/-/milestones, unless it has a "for:Dev" label)
• added an entry to CHANGELOG.md
• added a short text that can be used in the release notes (Is it important for release notes, its dev-stuff)
• [?] Once your MR has been merged, you are responsible to create a testing issue in the Beta Testing forum: https://foodsharing.de/?page=bezirk&bid=734&sub=forum. Please change the MRs label to "state:Beta testing".
  • Consider writing a detailed description in German.
  • Describe in a few sentences, what should be tested from a user perspective.
  • Also mention different settings (e.g. different browsers, roles, ...) how this change can be tested.
  • Be aware, that also non technical people should understand.

Release notes text in German

Closes #1302 (closed)