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-bot-mjolnir/templates/systemd/matrix-bot-mjolnir.service.j2

@@ -0,0 +1,42 @@
+#jinja2: lstrip_blocks: "True"
+[Unit]
+Description=Matrix Mjolnir bot
+{% for service in matrix_bot_mjolnir_systemd_required_services_list %}
+Requires={{ service }}
+After={{ service }}
+{% endfor %}
+{% for service in matrix_bot_mjolnir_systemd_required_services_list %}
+Wants={{ service }}
+{% endfor %}
+DefaultDependencies=no
+
+[Service]
+Type=simple
+Environment="HOME={{ matrix_systemd_unit_home_path }}"
+ExecStartPre=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} kill matrix-bot-mjolnir 2>/dev/null || true'
+ExecStartPre=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} rm matrix-bot-mjolnir 2>/dev/null || true'
+
+# Intentional delay, so that the homeserver (we likely depend on) can manage to start.
+ExecStartPre={{ matrix_host_command_sleep }} 5
+
+ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-bot-mjolnir \
+			--log-driver=none \
+			--user={{ matrix_user_uid }}:{{ matrix_user_gid }} \
+			--cap-drop=ALL \
+			--read-only \
+			--network={{ matrix_docker_network }} \
+			--mount type=bind,src={{ matrix_bot_mjolnir_config_path }},dst=/data/config,ro \
+			--mount type=bind,src={{ matrix_bot_mjolnir_data_path }},dst=/data \
+			{% for arg in matrix_bot_mjolnir_container_extra_arguments %}
+			{{ arg }} \
+			{% endfor %}
+			{{ matrix_bot_mjolnir_docker_image }}
+
+ExecStop=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} kill matrix-bot-mjolnir 2>/dev/null || true'
+ExecStop=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} rm matrix-bot-mjolnir 2>/dev/null || true'
+Restart=always
+RestartSec=30
+SyslogIdentifier=matrix-bot-mjolnir
+
+[Install]
+WantedBy=multi-user.target