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-appservice-slack/templates/config.yaml.j2

@@ -0,0 +1,35 @@
+#jinja2: lstrip_blocks: True
+slack_hook_port: {{ matrix_appservice_slack_slack_port }}
+inbound_uri_prefix: "{{ matrix_appservice_slack_inbound_uri_prefix }}"
+bot_username: "{{ matrix_appservice_slack_bot_name }}"
+username_prefix: {{ matrix_appservice_slack_user_prefix }}
+
+homeserver:
+    server_name: "{{ matrix_domain }}"
+    url: "{{ matrix_appservice_slack_homeserver_url }}"
+    media_url: "{{ matrix_appservice_slack_homeserver_media_url }}"
+
+# Real Time Messaging API (RTM)
+# Optional if slack_hook_port and inbound_uri_prefix are defined, required otherwise.
+#
+rtm:
+  # Use the RTM API to listen for requests, which does not require
+  # the bridge to listen on the hook port.
+  # You should leave this enabled, unless you plan to use the
+  # bridge exclusively for webhooks.
+  #
+  enable: true
+
+  # Logging level specific to RTM traffic.
+  #
+  log_level: "silent"
+
+{% if matrix_appservice_slack_database_engine == 'nedb' %}
+dbdir: "/data"
+{% else %}
+db:
+    engine: {{ matrix_appservice_slack_database_engine|to_json }}
+    connectionString: {{ matrix_appservice_slack_database_connectionString|to_json }}
+{% endif %}
+
+matrix_admin_room: "{{ matrix_appservice_slack_control_room_id }}"