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-jitsi/templates/web/custom-config.js.j2

@@ -0,0 +1,18 @@
+config.defaultLanguage = {{ matrix_jitsi_web_config_defaultLanguage|to_json }};
+
+
+if (!config.hasOwnProperty('p2p')) config.p2p = {% raw %}{}{% endraw %};
+
+{% if matrix_jitsi_web_stun_servers|length > 0 %}
+config.p2p.stunServers = [
+	{% for url in matrix_jitsi_web_stun_servers %}
+		{ urls: {{ url|to_json }} }{% if not loop.last %},{% endif %}
+	{% endfor %}
+];
+{% endif %}
+
+{% if matrix_jitsi_etherpad_enabled %}
+config.etherpad_base = {{ (matrix_jitsi_etherpad_base + '/p/') |to_json }}
+{% endif %}
+
+{{ matrix_jitsi_web_custom_config_extension }}