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/files/frigate-exporter.container

@@ -0,0 +1,18 @@
+# vim: set ft=systemd :
+[Unit]
+Description=Prometheus exporter for Frigate
+After=network.target
+Wants=network.target
+After=frigate.service
+
+[Container]
+Image=git.pyrocufflink.net/containerimages/prometheus-frigate-exporter
+Pull=never
+Environment=FRIGATE_STATS_URL=http://localhost:5000/api/stats
+User=45005
+Group=45005
+NoNewPrivileges=true
+Network=host
+
+[Install]
+WantedBy=multi-user.target