This moves the comments from being just in Jinja,
to actually ending up in the generated `labels` file,
which makes inspection of the final result easier.
Also, some new lines were added here and there to make labels
more legible.
The generated file may still include weird new-lines due to
various `if` statements yielding content or not, but that's not so ugly
anymore - now that we have proper start/end sections that are visible in
the final `labels` file.
We'd be adding integration with an internal Traefik entrypoint
(`matrix_playbook_internal_matrix_client_api_traefik_entrypoint`),
so renaming helps disambiguate things.
There's no need for deperecation tasks, because the old names
have only been part of this `bye-bye-nginx-proxy` branch and not used by
anyone publicly.
This is an attempt at optimizing service startup.
The effect is most pronounced when many services are restarted one by one.
The systemd service manager role sometimes does this - for example when `just install-service synapse` runs.
In such cases, a 5-second delay for each Synapse worker service
(or other bridge/bot service that waits on the homeserver) quickly adds up to a lot.
When services are all stopped fully and then started, the effect is not so pronounced, because
`matrix-synapse.service` starts first and pulls all worker services (defined as `Wants=` for it).
Later on, when the systemd service manager role "starts" these worker services, they're started already.
Even if they had a 5-second wait each, it would have happened in parallel.
