Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/4445

This commit adds copyright attributions in SPDX to the files for matrix-client-fluffychat, 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.

* add FluffyChat

* capitalization

* Update group_vars/matrix_servers

Co-authored-by: Slavi Pantaleev <slavi@devture.com>

* fix link in readme

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Co-authored-by: Slavi Pantaleev <slavi@devture.com>