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.

docs/configuring-playbook-ma1sd.md

@@ -33,7 +33,7 @@ matrix_ma1sd_matrixorg_forwarding_enabled: true
 ## Customizing email templates
 
 If you'd like to change the default email templates used by ma1sd, take a look at the `matrix_ma1sd_threepid_medium_email_custom_` variables
-(in the `roles/matrix-ma1sd/defaults/main.yml` file.
+(in the `roles/custom/matrix-ma1sd/defaults/main.yml` file.
 
 
 ## ma1sd-controlled Registration
@@ -86,7 +86,7 @@ You can refer to the [ma1sd website](https://github.com/ma1uta/ma1sd) for more d
 
 To use a more custom configuration, you can define a `matrix_ma1sd_configuration_extension_yaml` string variable
 and put your configuration in it.
-To learn more about how to do this, refer to the information about `matrix_ma1sd_configuration_extension_yaml` in the [default variables file](../roles/matrix-ma1sd/defaults/main.yml) of the ma1sd component.
+To learn more about how to do this, refer to the information about `matrix_ma1sd_configuration_extension_yaml` in the [default variables file](../roles/custom/matrix-ma1sd/defaults/main.yml) of the ma1sd component.
 
 ## Example: SMS verification