The playbook exposes service metrics under a single endpoint
(`https://matrix.example.com/metrics/*`), controlled by
`matrix_metrics_exposure_enabled` and friends. ntfy was not wired into
this at all, so enabling metrics exposure did not expose ntfy's metrics
and enabling Basic Authentication did not protect them.

We have ntfy serve its metrics on a dedicated port, instead of on its
regular HTTP port. Serving them on the regular HTTP port also makes them
reachable at `https://ntfy.example.com/metrics`, where nothing protects
them, as ntfy does not apply its own access-control rules to the metrics
endpoint.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/5468

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>