Rework all roles to include component_(docker|container)_image_registry_prefix* variables

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.

roles/custom/matrix-synapse-usage-exporter/tasks/main.yml

@@ -6,6 +6,9 @@
     - install-all
     - install-synapse-usage-exporter
   block:
+    - when: matrix_synapse_usage_exporter_enabled | bool
+      ansible.builtin.include_tasks: "{{ role_path }}/tasks/validate_config.yml"
+
     - when: matrix_synapse_usage_exporter_enabled | bool
       ansible.builtin.include_tasks: "{{ role_path }}/tasks/setup_install.yml"