Related to 8005557061

Running with a user (like `matrix:matrix`) fails if Etherpad is enabled,
because `/matrix/etherpad` is owned by `matrix_etherpad_user_uid`/`matrix_etherpad_user_gid` (`5001:5001`).

The `matrix` user can't acccess the Etherpad directory for this reason
and Borgmatic fails when trying to make a backup.

There may be other things under `/matrix` which similarly use
non-`matrix:matrix` permissions.

Another workaround might have been to add `/matrix/etherpad` (and
potentially other things) to `matrix_backup_borg_location_exclude_patterns`, but:

- that means Etherpad won't be backed up - not great
- only excluding Etherpad may not be enough. There may be other files we
  need to exclude as well

---

Running with `root` is still not enough though.

We need at least the `CAP_DAC_OVERRIDE` capability, or we won't be able to read the
`/etc/borgmatic.d/config.yaml` configuration file (owned by
`matrix:matrix` with `0640` permissions).

---

Additionally, it seems like the backup process tries to write to at least a few directories:
- `/root/.borgmatic`
- `/root/.ssh`
- `/root/.config`

> [Errno 30] Read-only file system: '/root/.borgmatic'
> Error while creating a backup.
> /etc/borgmatic.d/config.yaml: Error running configuration file

We either need to stop mounting the container filesystem as readonly
(remove `--read-only`) or to allow writing via a `tmpfs`.

I've gone the `tmpfs` route which seems to work.

In any case, the mounted source directories (`matrix_backup_borg_location_source_directories`)
are read-only regardless, so our actual source files are protected from unintentional changes.

Without this, it's a string and borg says:

> At 'hooks.postgresql_databases[INDEX_HERE].port': '5432' is not of type 'integer'
> /etc/borgmatic/config.yaml /etc/borgmatic.d /tmp/.config/borgmatic/config.yaml /tmp/.config/borgmatic.d: No valid configuration files found

.. and fails to do anything.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2257

Fixed in d134cd7c4c
(thanks to `alpine:latest` now being `alpine:3.17.0`, which includes
Postgres v15)

This is done via devture_systemd_service_manager_services_list_auto
already.

- forego removing Docker images - it's not effective anyway, because it
  only removes the last version.. which is a drop in the bucket, usually

- do not reload systemd - it's none of our business. `--tags=start`,
  etc., handle this

- combine all uninstall tasks under a single block, which only runs if
  we detect traces (a leftover systemd .service file) of the component.
  If no such .service is detected, we skip them all. This may lead to
  incorect cleanup in rare cases, but is good enough for the most part.

This paves the way for installing other roles into `roles/galaxy` using `ansible-galaxy`,
similar to how it's done in:

- https://github.com/spantaleev/gitea-docker-ansible-deploy
- https://github.com/spantaleev/nextcloud-docker-ansible-deploy

In the near future, we'll be removing a lot of the shared role code from here
and using upstream roles for it. Some of the core `matrix-*` roles have
already been extracted out into other reusable roles:

- https://github.com/devture/com.devture.ansible.role.postgres
- https://github.com/devture/com.devture.ansible.role.systemd_docker_base
- https://github.com/devture/com.devture.ansible.role.timesync
- https://github.com/devture/com.devture.ansible.role.vars_preserver
- https://github.com/devture/com.devture.ansible.role.playbook_runtime_messages
- https://github.com/devture/com.devture.ansible.role.playbook_help

We just need to migrate to those.