[MateoLostanlen]

Part of pyronear/roadmap#16, fixes #445 (API reboot step). Stacked on #458.

• The stuck detector only caught a PTZ whose poses all look alike, every 30 min. It now checks every camera every 5 min for three problems: no new image, new images with the exact same pixels (frozen camera, each pose on its own image as at Epinay), and the existing turret not moving check.
• Two checks in a row reboot the camera through its API, at most 3 attempts per 24 h and 30 min apart. Cameras that cannot reboot are only logged. Power cuts stay with the Shelly watchdog.
• /patrol_status exposes the detected problem and the reboot attempts, for monitoring.
• ALLOW_STILL_CAMERA=true (testing only, warned at startup) ignores frozen and not moving cameras, to work with a still PTZ at home.