We had to remove UID/GID environment variables that we used to pass
to the Synapse container, because it was causing a problem after
https://github.com/matrix-org/synapse/pull/11209

We were using both `--user` and UID/GID environment variables until now.

Until now, we were leaving services "enabled"
(symlinks in /etc/systemd/system/multi-user.target.wants/).

We clean these up now. Broken symlinks may still exist in older
installations that enabled/disabled services. We're not taking care
to fix these up. It's just a cosmetic defect anyway.

It's mildly annoying when trying to execute these scripts while logged
in as a regular user, as the missing execute permissions will hinder
autocompletion even when trying to use with sudo.

These shell scripts don't contain secrets, but may fail when ran by a
regular user. The failure is due to the lack of access to the /matrix
directory, and does not result in any damage.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1070

Adding more presets in the future would be nice.

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`).

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.

`-v` magically creates the source destination as a directory,
if it doesn't exist already. We'd like to avoid this magic
and the potential breakage that it might cause.

We'd rather fail while Docker tries to find things to `--mount`
than have it automatically create directories and fail anyway,
while having contaminated the filesystem.

There's a lot more `-v` instances remaining to be fixed later on.
This is just some start.

Things like `matrix_synapse_container_additional_volumes` and
`matrix_nginx_proxy_container_additional_volumes` were not changed to
use `--mount`, as options for each one are passed differently
(`ro` is `ro`, but `rw` doesn't exist and `slave` is `bind-propagation=slave`).
To avoid breaking people's custom volume mounts, we keep it as it is for now.

A deficiency with `--mount` is that it lacks the `z` option (SELinux
ownership changes), and some of our `-v` instances use that. I'm not
sure how supported SELinux is for us right now, but it might be,
and breaking that would not be a good idea.

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.

No migration steps should be required.

Attempt at fixing #268 (Github Issue)

We do use some `:latest` images by default for the following services:
- matrix-dimension
- Goofys (in the matrix-synapse role)
- matrix-bridge-appservice-irc
- matrix-bridge-appservice-discord
- matrix-bridge-mautrix-facebook
- matrix-bridge-mautrix-whatsapp

It's terribly unfortunate that those software projects don't release
anything other than `:latest`, but that's how it is for now.

Updating that software requires that users manually do `docker pull`
on the server. The playbook didn't force-repull images that it already
had.

With this patch, it starts doing so. Any image tagged `:latest` will be
force re-pulled by the playbook every time it's executed.

It should be noted that even though we ask the `docker_image` module to
force-pull, it only reports "changed" when it actually pulls something
new. This is nice, because it lets people know exactly when something
gets updated, as opposed to giving the indication that it's always
updating the images (even though it isn't).