As seen on TV:
https://github.com/matrix-org/synapse/blob/master/docs/metrics-howto.md#monitoring-workers

(until https://github.com/matrix-org/synapse/issues/8787 is resolved)

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/716

This patch makes us use more fully-qualified container image names
(either prefixed with docker.io/ or with localhost/).

The latter happens when self-building is enabled.

We've recently had issues where if an image was removed manually
and the service was restarted (making `docker run` fetch it from Docker Hub, etc.),
we'd end up with a pulled image, even though we're aiming for a self-built one.
Re-running the playbook would then not do a rebuild, because:
- the image with that name already exists (even though it's something
else)
- we sometimes had conditional logic where we'd build only if the git
repo changed

By explicitly changing the name of the images (prefixing with localhost/),
we avoid such confusion and the possibility that we'd automatically pul something
which is not what we expect.

Also, I've removed that condition where building would happen on git
changes only. We now always build (unless an image with that name
already exists). We just force-build when the git repo changes.

(yes, a bit awkward and brittle… xD)

.. alphabetically and put those not documented as multi-instance
capable on ports ending on zero.

Fixes #586 (Github Issue)

Fixes #579 (Github Issue).

Fixes #539 (Github Issue).

There's no change in the source code. Just a release bump for packaing
reasons. It doesn't matter much for us here, but let's be on the latest
tag anyway.

· needs documentation; no checks yet for port clashes or typos in worker name
· according to https://github.com/matrix-org/synapse/wiki/Workers-setup-with-nginx#results
  about 90% of requests go to the synchrotron endpoint
· thus, the synchrotron worker is especially suited to be load-balanced
· most of the other workers are documented to support only a single instance
· https://github.com/matrix-org/synapse/blob/master/docs/workers.md

This keeps the roles cleaner and more independent of matrix-base,
which may be important for people building their own playbook
out of the individual roles and not using the matrix-base role.