Change Role of User in Project or Group does not send System hook

Summary

If a new user is added to a Project or Group then the system hooks user_add_to_group and user_add_to_team are sent out. These include the access_level (Role) of the User. If now the Role of the User is changes (without removing and adding the user again) there is no system hook at all and an external system might never know that the role has been changed.

Steps to reproduce

1. Configure System Hooks in Gitlab
2. Add User to Group with Role Developer (user_add_to_group webhook is sent)
3. Change Role of User to Maintainer
4. No webhook is sent.

What is the current bug behavior?

No Webhooks are sent

What is the expected correct behavior?

A: Add a new system hook which informs an external system about the changed Role

B: send the user_remove_from_group and right after it the user_add_to_group with the correct Role (this might be more a bit a workaround but could work)