This commit adds copyright attributions in SPDX to the files for matrix-client-cinny, following REUSE's specification.

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

This:

- brings consistency - no more mixing `_name_prefix` and `_registry_prefix`
- adds extensibility - a future patch will allow reconfiguring all registry prefixes for all roles in the playbook

We still have `_docker_` vs `_container_` inconsistencies.
These may be worked on later.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3701

We can restore support for it by making a non-/ path prefix trigger a
self-build with a modified build config, so that a Cinny version with
path-prefix support would be produced. Traefik label changes may also be
required.

For now, we're not doing all that work, but simply dropping support for path
prefixes for Cinny.

Putting each client into its own network was good for isolation,
but it's quite wasteful in terms of the container network pool.

Previously, it had to go through matrix-nginx-proxy.
It's exposed to Traefik directly via container labels now

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.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1939