Create experimental API endpoints to manage customizable roles

Fourth step based on the technical discovery:

create UI to edit the Role (weight: 5) / or just API as the description suggests (weight: 3)

The experimental API endpoints should support creating listing, creating, and deleting customizable roles:

• GET /groups/:id/member_roles
• POST /groups/:id/member_roles
• DELETE /groups/:id/member_roles/:id

These operations should only be allowed on the root group level.

This page may contain information related to upcoming products, features and functionality. It is important to note that the information presented is for informational purposes only, so please do not rely on the information for purchasing or planning purposes. Just like with all projects, the items mentioned on the page are subject to change or delay, and the development, release, and timing of any products, features, or functionality remain at the sole discretion of GitLab Inc.