better logging in rstp frame grabber

[romerocesar]

sometimes there are issues reading frames from the office cameras that result in errors like this one

{"name": "groundlight.stream", "level": "ERROR", "file": "/src/grabber.py", "line": 134, "function": "grab", "time": "2022-07-18 21:39:49,178", "asctime": "2022-07-18 21:39:49,178", "created": 1658180389.178412, "message": "could not read frame from self.capture=<VideoCapture 0x7f6d633490>"}

betters logs would help us troubleshoot and confirm whether the corresponding rtsp stream is actually working as expected