Update response codes
Change 202 response code to 200/201/204 since our APIs are not asynchronous.
Summary:
- CreateGroup -> "201 Created"
- ListGroup -> "200 OK"
- DeleteGroup -> "204 No Content"
- ListMember -> "200 OK"
- AddMember -> "200 OK"
- RemoveMember -> "204 No Content"
- UpdateGroup -> "200 OK"