api/rest: Add support for the submitter filter

Similar to commit 70f96f9 ("support the delegate filter for REST
API") which added the delegate filter this implements an exact match
only and not (as promised by `pwclient list -h`) as substring match.

But for the same reason as for the delegate filter this is better than
ignoring a passed submitter.

Author: ukleinek

pwclient/api.py

@@ -760,6 +760,9 @@ def patch_list(
         if archived is not None:
             filters['archived'] = archived
 
+        if submitter is not None:
+            filters['submitter'] = submitter
+
         if delegate is not None:
             filters['delegate'] = delegate