Add diff mode for ec2_group (#44533)

* Add (preview) diff mode support ec2_group

* Add diff mode to some ec2_group integration tests

* Remove unnecessary arguments and add comment to the module notes

* Add changelog

lib/ansible/module_utils/aws/core.py

@@ -117,6 +117,7 @@ class AnsibleAWSModule(object):
                 msg='Python modules "botocore" or "boto3" are missing, please install both')
 
         self.check_mode = self._module.check_mode
+        self._diff = self._module._diff
         self._name = self._module._name
 
     @property