Fix healthcheck on stopping (#18476)

frigate/app.py

@@ -6,6 +6,7 @@ import secrets
 import shutil
 from multiprocessing import Queue
 from multiprocessing.synchronize import Event as MpEvent
+from pathlib import Path
 from typing import Optional
 
 import psutil
@@ -685,6 +686,9 @@ class FrigateApp:
     def stop(self) -> None:
         logger.info("Stopping...")
 
+        # used by the docker healthcheck
+        Path("/dev/shm/.frigate-is-stopping").touch()
+
         self.stop_event.set()
 
         # set an end_time on entries without an end_time before exiting