fix(snapshots): warn if no snapshots could be found

backupbot.py

@@ -179,9 +179,16 @@ def restore(snapshot, target, noninteractive):
 @cli.command()
 def snapshots():
     snapshots = restic.snapshots()
+    no_snapshots = True
     for snap in snapshots:
         if not SERVICE or (tags := snap.get('tags')) and SERVICE in tags:
             print(snap['time'], snap['id'])
+            no_snapshots = False
+    if no_snapshots:
+        err_msg = "No Snapshots found"
+        if SERVICE:
+            err_msg += f' for app {SERVICE}'
+        logging.warning(err_msg)
 
 
 @cli.command()