This is done for a few reasons:

- less globals and more indepdendence for each role is better. We rely
  on various externally-hosted roles and they don't rely on this global
  either.

- `matrix_container_global_registry_prefix` could make people think they
  could just override this variable and have all their images pull from
  elsewhere. This is rarely the case, unless you've taken special care
  to mirror all the various components (from their respective
  registries) to your own. In such a case, you probably know what you're
  mirroring and can adjust individual variables.

- nowadays, various components live on different registries.
  With Docker Inc tightening rate limits for Docker Hub, it's even more
  likely that we'll see increased diversity in where images are hosted

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

Related to 0241c71a4c

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/3270#issuecomment-2143782962

With this change, it should be possible for people to adjust the Docker
dependency from `docker.service` to something else (e.g. `pkg-ContainerManager-dockerd.service`),
or to completely eliminate it by setting `devture_systemd_docker_base_docker_service_name` to an empty string.

This makes it easier for people to use the playbook against a Synology DSM server.

This is actually authored by Julian Foad here
(https://lab.trax.im/matrix/matrix-docker-ansible-deploy), but was in
need of a rebase and various adjustments caused by huge playbook
refactoring that landed in the past months.

This rework is completely untested.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/266