added username for uniqueness of connection db entry

backend/src/main/java/com/vaessl/app/connection/ConnectionProvider.java

@@ -9,6 +9,8 @@ public interface ConnectionProvider {
 
     ConnectionResponse authenticate(ConnectionRequest request);
 
+    ConnectionEntity findUniqueConnectionEntry(ConnectionRequest request);
+
     ConnectionEntity connectionToEntity(ConnectionRequest request, ConnectionResponse response);
 
     void updateToRepository(ConnectionEntity existing, ConnectionResponse response);