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-mailer/templates/env-mailer.j2

@@ -0,0 +1,9 @@
+#jinja2: lstrip_blocks: "True"
+{% if matrix_mailer_relay_use %}
+SMARTHOST={{ matrix_mailer_relay_host_name }}::{{ matrix_mailer_relay_host_port }}
+{% endif %}
+{% if matrix_mailer_relay_auth %}
+SMTP_USERNAME={{ matrix_mailer_relay_auth_username }}
+SMTP_PASSWORD={{ matrix_mailer_relay_auth_password }}
+{% endif %}
+HOSTNAME={{ matrix_mailer_hostname }}

roles/custom/matrix-mailer/templates/systemd/matrix-mailer.service.j2

@@ -0,0 +1,37 @@
+#jinja2: lstrip_blocks: "True"
+[Unit]
+Description=Matrix mailer
+After=docker.service
+Requires=docker.service
+DefaultDependencies=no
+
+[Service]
+Type=simple
+Environment="HOME={{ matrix_systemd_unit_home_path }}"
+ExecStartPre=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} kill matrix-mailer 2>/dev/null || true'
+ExecStartPre=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} rm matrix-mailer 2>/dev/null || true'
+
+# --hostname gives us a friendlier hostname than the default.
+# The real hostname is passed via a `HOSTNAME` environment variable though.
+ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-mailer \
+			--log-driver=none \
+			--user={{ matrix_mailer_container_user_uid }}:{{ matrix_mailer_container_user_gid }} \
+			--cap-drop=ALL \
+			--read-only \
+			--tmpfs=/var/spool/exim:rw,noexec,nosuid,size=100m \
+			--network={{ matrix_docker_network }} \
+			--env-file={{ matrix_mailer_base_path }}/env-mailer \
+			--hostname=matrix-mailer \
+			{% for arg in matrix_mailer_container_extra_arguments %}
+			{{ arg }} \
+			{% endfor %}
+			{{ matrix_mailer_docker_image }}
+
+ExecStop=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} kill matrix-mailer 2>/dev/null || true'
+ExecStop=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} rm matrix-mailer 2>/dev/null || true'
+Restart=always
+RestartSec=30
+SyslogIdentifier=matrix-mailer
+
+[Install]
+WantedBy=multi-user.target