add log when probing detect stream on startup

when users don't explicitly set detect.width and detect.height, we probe for them. sometimes the probe hangs (camera doesn't support UDP, like some Reolinks), so this log message will make that clearer

frigate/config/config.py

@@ -730,6 +730,9 @@ class FrigateConfig(FrigateBaseModel):
                 )
 
                 if need_detect_dimensions:
+                    logger.info(
+                        f"detect.width and detect.height not set for {camera_config.name}, probing detect stream to determine resolution."
+                    )
                     stream_info = {"width": 0, "height": 0, "fourcc": None}
                     try:
                         stream_info = stream_info_retriever.get_stream_info(