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-user-creator/defaults/main.yml

@@ -0,0 +1,22 @@
+---
+
+# matrix-user-creator is a role that aims to automate initial Matrix user account creation.
+#
+# This role only supports initial user account creation and will not manage subsequent user-type changes
+# or password changes.
+#
+# The playbook registers various bot user accounts automatically using this role by injecting
+# user creation definitions into the `matrix_user_creator_users_auto` variable.
+#
+# To get started creating your own Matrix user accounts, use the `matrix_user_creator_users_additional` variable.
+
+# matrix_user_creator_users_auto holds a list of users that should be created on the Matrix homeserver.
+# The playbook adds some user definitions here to have them end up in `matrix_user_creator_users` (see `vars/main.yml`) and get automatically created.
+# This value is influenced by the playbook and will be overwritten elsewhere (`group_vars/`, etc.)
+# To add your own user definitions, use the `matrix_user_creator_users_additional` variable.
+matrix_user_creator_users_auto: []
+
+# matrix_user_creator_users_additional holds a list of users that should be created on the Matrix homeserver.
+# Add your own users here to have them end up in `matrix_user_creator_users` (see `vars/main.yml`) and get automatically created.
+# For example syntax for this variable, see the documentation for `matrix_user_creator_users` in `vars/main.yml`.
+matrix_user_creator_users_additional: []