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-bridge-hookshot.md

@@ -14,12 +14,12 @@ Note: the playbook also supports [matrix-appservice-webhooks](configuring-playbo
 Refer to the [official instructions](https://matrix-org.github.io/matrix-hookshot/latest/setup.html) to learn what the individual options do.
 
 1. Enable the bridge by adding `matrix_hookshot_enabled: true` to your `vars.yml` file
-2. For each of the services (GitHub, GitLab, Jira, Figma, generic webhooks) fill in the respective variables `matrix_hookshot_service_*` listed in [main.yml](/roles/matrix-bridge-hookshot/defaults/main.yml) as required.
+2. For each of the services (GitHub, GitLab, Jira, Figma, generic webhooks) fill in the respective variables `matrix_hookshot_service_*` listed in [main.yml](/roles/custom/matrix-bridge-hookshot/defaults/main.yml) as required.
 3. Take special note of the `matrix_hookshot_*_enabled` variables. Services that need no further configuration are enabled by default (GitLab, Generic), while you must first add the required configuration and enable the others (GitHub, Jira, Figma).
 4. If you're setting up the GitHub bridge, you'll need to generate and download a private key file after you created your GitHub app. Copy the contents of that file to the variable `matrix_hookshot_github_private_key` so the playbook can install it for you, or use one of the [other methods](#manage-github-private-key-with-matrix-aux-role) explained below.
 5. If you've already installed Matrix services using the playbook before, you'll need to re-run it (`--tags=setup-all,start`). If not, proceed with [configuring other playbook services](configuring-playbook.md) and then with [Installing](installing.md). Get back to this guide once ready. Hookshot can be set up individually using the tag `setup-hookshot`.
 
-Other configuration options are available via the `matrix_hookshot_configuration_extension_yaml` and `matrix_hookshot_registration_extension_yaml` variables, see the comments in [main.yml](/roles/matrix-bridge-hookshot/defaults/main.yml) for how to use them.
+Other configuration options are available via the `matrix_hookshot_configuration_extension_yaml` and `matrix_hookshot_registration_extension_yaml` variables, see the comments in [main.yml](/roles/custom/matrix-bridge-hookshot/defaults/main.yml) for how to use them.
 
 Finally, run the playbook (see [installing](installing.md)).
 
@@ -54,14 +54,14 @@ Unless indicated otherwise, the following endpoints are reachable on your `matri
 | widgets | `/hookshot/widgetapi/` | `matrix_hookshot_widgets_endpoint` | Widgets |
 | metrics | `/metrics/hookshot` | `matrix_hookshot_metrics_enabled` and `matrix_hookshot_metrics_proxying_enabled`. Requires `/metrics/*` endpoints to also be enabled via `matrix_nginx_proxy_proxy_matrix_metrics_enabled` (see the `matrix-nginx-proxy` role). Read more in the [Metrics section](#metrics) below. | Prometheus |
 
-See also `matrix_hookshot_matrix_nginx_proxy_configuration` in [init.yml](/roles/matrix-bridge-hookshot/tasks/init.yml).
+See also `matrix_hookshot_matrix_nginx_proxy_configuration` in [init.yml](/roles/custom/matrix-bridge-hookshot/tasks/init.yml).
 
-The different listeners are also reachable *internally* in the docker-network via the container's name (configured by `matrix_hookshot_container_url`) and on different ports (e.g. `matrix_hookshot_appservice_port`). Read [main.yml](/roles/matrix-bridge-hookshot/defaults/main.yml) in detail for more info.
+The different listeners are also reachable *internally* in the docker-network via the container's name (configured by `matrix_hookshot_container_url`) and on different ports (e.g. `matrix_hookshot_appservice_port`). Read [main.yml](/roles/custom/matrix-bridge-hookshot/defaults/main.yml) in detail for more info.
 
 ### Manage GitHub Private Key with matrix-aux role
 
 The GitHub bridge requires you to install a private key file. This can be done in multiple ways:
-- copy the *contents* of the downloaded file and set the variable `matrix_hookshot_github_private_key` to the contents (see example in [main.yml](/roles/matrix-bridge-hookshot/defaults/main.yml)).
+- copy the *contents* of the downloaded file and set the variable `matrix_hookshot_github_private_key` to the contents (see example in [main.yml](/roles/custom/matrix-bridge-hookshot/defaults/main.yml)).
 - somehow copy the file to the path `{{ matrix_hookshot_base_path }}/{{ matrix_hookshot_github_private_key_file }}` (default: `/matrix/hookshot/private-key.pem`) on the server manually.
 - use the `matrix-aux` role to copy the file from an arbitrary path on your ansible client to the correct path on the server.
 
@@ -74,7 +74,7 @@ matrix_aux_file_definitions:
     owner: "{{ matrix_user_username }}"
     group: "{{ matrix_user_groupname }}"
 ```
-For more info see the documentation in the [matrix-aux base configuration file](/roles/matrix-aux/defaults/main.yml).
+For more info see the documentation in the [matrix-aux base configuration file](/roles/custom/matrix-aux/defaults/main.yml).
 
 ### Provisioning API