Restrict stopping core during migrations with force option (#5205)

supervisor/exceptions.py

@@ -1,4 +1,5 @@
 """Core Exceptions."""
+
 from collections.abc import Callable
 
 
@@ -339,6 +340,12 @@ class APIAddonNotInstalled(APIError):
     """Not installed addon requested at addons API."""
 
 
+class APIDBMigrationInProgress(APIError):
+    """Service is unavailable due to an offline DB migration is in progress."""
+
+    status = 503
+
+
 # Service / Discovery