Share groups with groups (backend)

Overview

Groups are used for project organization, but another common use case is using them to organize people into teams. This works well - but when distributing project access to a group across many projects, access can only be granted project-by-project in the UI.

Since GitLab doesn't support sharing a group with a group, this means adding the group to individual projects. This is time-consuming, and GitLab should support sharing groups with groups.

Proposal

Add "Share with group" to Groups. We currently do this with Projects, and we should duplicate this approach with the "Select group to share with", "Max access level", and "Access expiration date" fields.

Current approach to sharing a project with a group:

OP by @Flipez

Description

Currently you can only share a project with a group.

Proposal

It would be nice to share a group with another group.

For example you maybe want the frontend team to view the backend code but not edit it. So you currently have to share privileges for each project. With this feature you could share the backend top-level group with guest permissions for the top-level frontend and all its subgroups.