Use graphql instead of REST API for member role UI
When we started implementing custom roles we implemented/changed REST API endpoints and started calling some of them from the frontend. The decision was done mostly because the whole project was started by an Backend Engineer who joined recently and was not aware of the fact we prefer GraphQL. We already agreed we want to convert fully to the graphQL.
Now we need to adjust the public API to accept both group and instance member roles and doing so for two different APIs seems to be needless. Therefore we should adjust only graphql. That also means, we need to change all the calls we do from frontend to the REST API to GraphQL.
The REST API endpoints that need to be replaced are located in this file: https://gitlab.com/gitlab-org/gitlab/-/blob/1c45bc7b99fbc0ed8de488de99871ba66f5fc9e7/ee/app/assets/javascripts/api/member_roles_api.js