Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/958

Adding more presets in the future would be nice.

Related to: https://matrix.org/blog/2021/02/18/synapse-1-27-0-released#dropping-armv7-docker-images

This give us the possibility to run multiple instances of
workers that that don't expose a port.

Right now, we don't support that, but in the future we could
run multiple `federation_sender` or `pusher` workers, without
them fighting over naming (previously, they'd all be named
something like `matrix-synapse-worker-pusher-0`, because
they'd all define `port` as `0`).

Related to:
- https://github.com/matrix-org/synapse/pull/9407
- https://github.com/matrix-org/synapse/pull/7855

This leads to much easier management and potential safety
features (validation). In the future, we could try to avoid port
conflicts as well, but it didn't seem worth the effort to do it now.
Our port ranges seem large enough.

This can also pave the way for a "presets" feature
(similar to `matrix_nginx_proxy_ssl_presets`) which makes it even easier
for people to configure worker counts.

This will make data migration easier.

There was a `matrix_nginx_proxy_enabled|default(False)` check, but:
- it didn't seem to work reliably for some reason (hmm)
- referring to a `matrix_nginx_proxy_*` variable from within the
  `matrix-synapse` role is not ideal
- exposing always happened on `127.0.0.1`, which may not be good enough
  for some rarer setups (where the own webserver is external to the host)

In short, this makes Synapse a 2nd class citizen,
preparing for a future where it's just one-of-many homeserver software
options.

We also no longer have a default Postgres superuser password,
which improves security.

The changelog explains more as to why this was done
and how to proceed from here.

Continuation of aa86e0dac65, now that ARM images are out.

Because the ARM images are not pushed yet, we hold back to v1.23.0
for now.

ma1sd requires the openid endpoints for certain functionality.
Example: 90b2b5301c/src/main/java/io/kamax/mxisd/auth/AccountManager.java (L67-L99)

If federation is disabled, we still need to expose these openid APIs on the
federation port.

Previously, we were doing similar magic for Dimension.
As per its documentation, when running unfederated, one is to enable
the openid listener as well. As per their recommendation, people
are advised to do enable it on the Client-Server API port
and use the `federationUrl` variable to override where the federation
port is (making federation requests go to the Client-Server API).

Because ma1sd always uses the federation port (unless you do some
DNS overwriting magic using its configuration -- which we'd rather not
do), it's better if we just default to putting the `openid` listener
where it belongs - on the federation port.

With this commit, we retain the "automatically enable openid APIs" thing
we've been doing for Dimension, but move it to the federation port instead.
We also now do the same thing when ma1sd is enabled.

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.