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 also removes the condition that made it use `latest` when
self-building is enabled.

v0.1.4 is expected to build correctly now, given that this issue is fixed:
https://github.com/matrix-org/rust-synapse-compress-state/issues/134

This saves us one container network in the ideal case.

The latest tagged release (v0.1.3) does not pin any versions in its
Dockerfile and as such fails to build right now.

The `main` branch of rust-synapse-compress-state has already addressed
this and is buildable, but there's no tagged release yet.

Reported here: https://github.com/matrix-org/rust-synapse-compress-state/issues/134

This provides an additional security benefit. The password won't leak in
the process list anymore.

It will, additionally, be connected to the devture-postgres network, if
devture-postgres is enabled.