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-backup-borg/tasks/setup_install.yml

@@ -10,7 +10,7 @@
     when: not matrix_postgres_enabled
 
   - ansible.builtin.import_role:
-      name: matrix-postgres
+      name: custom/matrix-postgres
       tasks_from: detect_existing_postgres_version
 
   - name: Fail if detected Postgres version is unsupported

roles/custom/matrix-bot-buscarron/tasks/setup_install.yml

@@ -21,7 +21,7 @@
               systemd_services_to_stop: ['matrix-bot-buscarron.service']
 
         - ansible.builtin.import_role:
-            name: matrix-postgres
+            name: custom/matrix-postgres
             tasks_from: migrate_db_to_postgres
 
         - ansible.builtin.set_fact:

roles/custom/matrix-bot-honoroit/tasks/setup_install.yml

@@ -21,7 +21,7 @@
               systemd_services_to_stop: ['matrix-bot-honoroit.service']
 
         - ansible.builtin.import_role:
-            name: matrix-postgres
+            name: custom/matrix-postgres
             tasks_from: migrate_db_to_postgres
 
         - ansible.builtin.set_fact:

roles/custom/matrix-bot-matrix-reminder-bot/tasks/setup_install.yml

@@ -22,7 +22,7 @@
               systemd_services_to_stop: ['matrix-bot-matrix-reminder-bot.service']
 
         - ansible.builtin.import_role:
-            name: matrix-postgres
+            name: custom/matrix-postgres
             tasks_from: migrate_db_to_postgres
 
         - ansible.builtin.set_fact:

roles/custom/matrix-bot-postmoogle/tasks/setup_install.yml

@@ -18,7 +18,7 @@
               systemd_services_to_stop: ['matrix-bot-postmoogle.service']
 
         - ansible.builtin.import_role:
-            name: matrix-postgres
+            name: custom/matrix-postgres
             tasks_from: migrate_db_to_postgres
 
         - ansible.builtin.set_fact: