Move roles/matrix* to roles/custom/matrix*

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.

roles/custom/matrix-bridge-mautrix-signal/templates/registration.yaml.j2

@@ -0,0 +1,18 @@
+#jinja2: lstrip_blocks: "True"
+id: signal
+as_token: "{{ matrix_mautrix_signal_appservice_token }}"
+hs_token: "{{ matrix_mautrix_signal_homeserver_token }}"
+namespaces:
+    users:
+    - exclusive: true
+      regex: '^@signal_.+:{{ matrix_mautrix_signal_homeserver_domain | regex_escape }}$'
+    - exclusive: true
+      regex: '^@{{ matrix_mautrix_signal_appservice_bot_username | regex_escape }}:{{ matrix_mautrix_signal_homeserver_domain | regex_escape }}$'
+    aliases:
+    - exclusive: true
+      regex: '^#signal_.+:{{ matrix_mautrix_signal_homeserver_domain | regex_escape }}$'
+url: {{ matrix_mautrix_signal_appservice_address }}
+# See https://github.com/mautrix/signal/issues/43
+sender_localpart: _bot_{{ matrix_mautrix_signal_appservice_bot_username }}
+rate_limited: false
+de.sorunome.msc2409.push_ephemeral: true