Add Prometheus exporter for go2rtc and Frigate stream health

Standalone Python exporter that polls go2rtc /api/streams and Frigate
/api/stats every 15s, tracking bytes_recv deltas to detect stalled
streams. Exposes metrics on port 9199 including stream_up,
bytes_per_second, consumers, and camera_fps.

monitoring/config.yaml

@@ -0,0 +1,20 @@
+go2rtc_url: "http://192.168.1.241:1985"
+frigate_url: "http://192.168.1.241:5000"
+
+poll_interval: 15
+request_timeout: 5
+metrics_port: 9199
+
+cameras:
+  - FPE
+  - Porch_Downstairs
+  - Front_Porch
+  - Driveway_door
+  - Street_side
+  - Backyard
+  - House_side
+  - Driveway
+  - BackDoor
+  - Parlor
+  - Livingroom
+  - WyzePanV3