r/frigate: Clean up Frigate role

* Switch to Quadlet-style `.container` for systemd unit
* Update to new image tag naming scheme (not arch-specific)
* Use environment variables for secrets
* Allow the entire `frigate_config` variable to be overridden

roles/frigate/vars/main.yml

@@ -1,6 +1,2 @@
 frigate_podman_packages:
 - podman
-frigate_config:
-  mqtt: '{{ frigate_mqtt }}'
-  detectors: '{{ frigate_detectors }}'
-  cameras: '{{ frigate_cameras }}'