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-ntfy/defaults/main.yml

@@ -0,0 +1,16 @@
+---
+matrix_ntfy_enabled: true
+
+matrix_ntfy_base_path: "{{ matrix_base_data_path }}/ntfy"
+
+matrix_ntfy_version: v1.27.2
+matrix_ntfy_docker_image: "{{ matrix_container_global_registry_prefix }}binwiederhier/ntfy:{{ matrix_ntfy_version }}"
+matrix_ntfy_docker_image_force_pull: "{{ matrix_ntfy_docker_image.endswith(':latest') }}"
+
+# Controls whether the container exposes its HTTP port (tcp/8080 in the container).
+#
+# Takes an "<ip>:<port>" or "<port>" value (e.g. "127.0.0.1:8768"), or empty string to not expose.
+matrix_ntfy_container_http_host_bind_port: ''
+
+# A list of extra arguments to pass to the container
+matrix_ntfy_container_extra_arguments: []