OZG-4089 provide api for persisting/loading answers

src/main/java/de/ozgcloud/nachrichten/postfach/PersistPostfachNachrichtService.java

@@ -44,4 +44,21 @@ public interface PersistPostfachNachrichtService {
 	String persistAttachment(String vorgangId, AttachmentFile attachment);
 
 	Stream<PostfachNachricht> findRueckfragen(String postfachId);
+
+	/**
+	 * Persists the given answer
+	 * 
+	 * @param answer       The given answer
+	 * @param rueckfrageId The ID of the original Rueckfrage
+	 * @return
+	 */
+	String persistAnswer(String rueckfrageId, PostfachNachricht answer);
+
+	/**
+	 * Returns all Answers given for the Rueckfrage identified by id
+	 * 
+	 * @param rueckfrageId ID of the Rueckfrage to load answers for.
+	 * @return all Answers
+	 */
+	Stream<PostfachNachricht> findAnswers(String rueckfrageId);
 }