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-email2matrix/templates/config.json.j2

@@ -0,0 +1,14 @@
+#jinja2: lstrip_blocks: "True"
+{
+	"Smtp": {
+		"ListenInterface": "0.0.0.0:2525",
+		"Hostname": {{ matrix_email2matrix_smtp_hostname|to_json }},
+		"Workers": 10
+	},
+	"Matrix": {
+		"Mappings": {{ matrix_email2matrix_matrix_mappings | to_nice_json }}
+	},
+	"Misc": {
+		"Debug": {{ matrix_email2matrix_misc_debug|to_json }}
+	}
+}