Related to:
- https://github.com/mautrix/meta/releases/tag/v0.4.0
- https://mau.fi/blog/2024-09-mautrix-release/

It seems like the new version does not support a `/metrics` endpoint.
We skip keep the Ansible variables, but they're not doing anything.

Shared Secret Auth double puppeting still works for these bridges, but
is deprecated and will go away in the future.

* Add link to database migration documentation.
* Correct configuration snippet to dict instead of str

Related to: https://github.com/mautrix/facebook/issues/332

Fixes: https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3138