r/frigate-exporter: Deploy Prometheus exporter

Frigate exports useful statistics natively, but in a custom JSON format.
There is a [feature request][0] to add support for Prometheus format,
but it's mostly being ignored.  A community member has created a
standalone process that converts the JSON format into Prometheus format,
though, which we can use.

[0]: https://github.com/blakeblackshear/frigate/issues/2266

roles/frigate-exporter/handlers/main.yml

@@ -0,0 +1,4 @@
+- name: restart frigate-exporter
+  service:
+    name: frigate-exporter
+    state: restarted