Sender-Callbacks

Closes #61 (closed)

Vorsicht: Realtiver MR zu MR !98 (merged). Dieser MR verändert !98 (merged) -> Erst diesen MR in !98 (merged) mergen, dann MR !98 (merged) in main mergen

spec/endpoints/submissions/index.yml

@@ -53,6 +53,9 @@ post:
         examples:
           Beispiel:
             $ref: '../../examples/create-submission.yml'
+  callbacks:
+    NewEvents:
+      $ref: '../../callbacks/new-events.yml'
   responses:
     '201':
       description: Created