fix(resp-tranformer) handle already existing headers

Now add will only add header/json if it does not exist, config `append` added to support adding new value to existing header/json. If header does not exist, a new one will be added. config `replace added to replace the value of existing header/json with new value

spec/unit/dao/entities_schemas_spec.lua

@@ -401,4 +401,4 @@ describe("Entities Schemas", function()
       }, errors)
     end)
   end)
-end)
+end)