Insert custom constraintViolationException

Signed-off-by: Melanie Retter <melanie.retter@bosch-si.com>

hawkbit-core/src/main/java/org/eclipse/hawkbit/exception/SpServerError.java

@@ -21,6 +21,10 @@ public enum SpServerError {
     *
     */
     SP_REPO_ENTITY_ALRREADY_EXISTS("hawkbit.server.error.repo.entitiyAlreayExists", "The given entity already exists in database"),
+    /**
+    *
+    */
+    SP_REPO_CONSTRAINT_VIOLATION("hawkbit.server.error.repo.constraintViolation", "The given entity cannot be saved due to Constraint Violation"),
     /**
      * 
      */