Research how to consolidate ProjectMember and GroupMember models

Consolidate the ProjectMember and GroupMember models into Member as much as possible. This means dealing with notifications, refresh_member_authorized_projects, etc

This can be done once we're towards the end of Consolidate Group and Project member management (&7054 - closed)

Availability and Testing

• No new E2E tests or updates needed at this time. Please run the e2e:package-and-test job on the related MR(s)