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-cactus-comments/templates/cactus_appservice.yaml.j2

@@ -0,0 +1,19 @@
+# A unique, user-defined ID of the application service which will never change.
+id: "Cactus Comments"
+
+# Where the cactus-appservice is hosted:
+url: "http://matrix-cactus-comments:{{ matrix_cactus_comments_container_port }}"
+
+# Unique tokens used to authenticate requests between our service and the
+# homeserver (and the other way). Use the sha256 hashes of something random.
+# CHANGE THESE VALUES.
+as_token: {{ matrix_cactus_comments_as_token | to_json }}
+hs_token: {{ matrix_cactus_comments_hs_token | to_json }}
+
+# The user id of the cactusbot which can be used to register and moderate sites
+sender_localpart: "{{ matrix_cactus_comments_user_id }}"
+
+namespaces:
+  aliases:
+    - exclusive: true
+      regex: "#comments_.*"