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/defaults/main.yml

@@ -0,0 +1,34 @@
+---
+# Project source code URL: https://github.com/devture/exim-relay
+
+matrix_mailer_enabled: true
+
+matrix_mailer_base_path: "{{ matrix_base_data_path }}/mailer"
+
+matrix_mailer_container_image_self_build: false
+matrix_mailer_container_image_self_build_repository_url: "https://github.com/devture/exim-relay"
+matrix_mailer_container_image_self_build_src_files_path: "{{ matrix_mailer_base_path }}/docker-src"
+matrix_mailer_container_image_self_build_version: "{{ matrix_mailer_docker_image.split(':')[1] }}"
+
+matrix_mailer_version: 4.95-r0-4
+matrix_mailer_docker_image: "{{ matrix_mailer_docker_image_name_prefix }}devture/exim-relay:{{ matrix_mailer_version }}"
+matrix_mailer_docker_image_name_prefix: "{{ 'localhost/' if matrix_mailer_container_image_self_build else matrix_container_global_registry_prefix }}"
+matrix_mailer_docker_image_force_pull: "{{ matrix_mailer_docker_image.endswith(':latest') }}"
+
+# The user/group that the container runs with.
+# These match the `exim` user/group within the container image.
+matrix_mailer_container_user_uid: 100
+matrix_mailer_container_user_gid: 101
+
+# A list of extra arguments to pass to the container
+matrix_mailer_container_extra_arguments: []
+
+matrix_mailer_hostname: "{{ matrix_server_fqn_matrix }}"
+
+matrix_mailer_sender_address: "matrix@{{ matrix_domain }}"
+matrix_mailer_relay_use: false
+matrix_mailer_relay_host_name: "mail.example.com"
+matrix_mailer_relay_host_port: 587
+matrix_mailer_relay_auth: false
+matrix_mailer_relay_auth_username: ""
+matrix_mailer_relay_auth_password: ""