Hookshot wants a trailing slash for this route.

If we let Hookshot redirect, it goes to `/widgetapi/v1/static/`,
instead of `/hookshot/widgetapi/v1/static/`, so we take this matter into our
own hands.

Public URLs are like: `/hookshot/widgetapi/v1/static/`
.. which get translated to requests for: `/widgetapi/v1/static/`

Previously, we were stripping the whole `/hookshot/widgetapi` prefix,
which is wrong.

Most of these files were defining a service, usually toward the end.
These lines have been moved upward.

Some components (mautrix-signal, mautrix-gmessages, etc.) were defining
a service conditionally (only if metrics are exposed, etc). This was
causing issues like these in the Traefik logs:

> level=error msg="service \"matrix-mautrix-twitter\" error: port is missing" providerName=docker container=matrix-mautrix-twitter-..

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.