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-bot-go-neb/tasks/validate_config.yml

@@ -0,0 +1,13 @@
+---
+
+- name: Fail if there's not at least 1 client
+  ansible.builtin.fail:
+    msg: >-
+      You need at least 1 client in the matrix_bot_go_neb_clients block.
+  when: matrix_bot_go_neb_clients is not defined or matrix_bot_go_neb_clients[0] is not defined
+
+- name: Fail if there's not at least 1 service
+  ansible.builtin.fail:
+    msg: >-
+      You need at least 1 service in the matrix_bot_go_neb_services block.
+  when: matrix_bot_go_neb_services is not defined or matrix_bot_go_neb_services[0] is not defined