Add a role to install 'ntfy' push-notification server.

This commit adds a 'matrix-ntfy' role that runs Ntfy server in Docker with
simple configuration, and plumbing to add the role to the playbook.

TODO: documentation, self-check, database persistence.

roles/matrix-base/defaults/main.yml

@@ -59,6 +59,9 @@ matrix_server_fqn_grafana: "stats.{{ matrix_domain }}"
 # This is where you access the Sygnal push gateway.
 matrix_server_fqn_sygnal: "sygnal.{{ matrix_domain }}"
 
+# This is where you access the ntfy push notification service.
+matrix_server_fqn_ntfy: "ntfy.{{ matrix_domain }}"
+
 matrix_federation_public_port: 8448
 
 # The architecture that your server runs.