On removal or deletion of a user in a schedule, trigger rotation change & send email to Owners & Rotation participants

Problem to Solve

Being on-call is a critical function. Users plan their lives around being on-call, making themselves available to respond to incidents in real-time.

When someone is in an on-call schedule, we need to be mindful of what happens when:

• A user is removed from a project
• A user is removed from a Group
• A user is deactivated in GitLab as a whole

If a User is in an on-call schedule when one of the above events occurs, it will put their on-call response team and the services they are responsible for at risk of downtime.

The scope of this issue is to update the affected rotations.

Proposal

Update the rotation as though the user was removed. Rotation will recalculate. Send an email to the Projects owners and all participants in the rotation saying:

User W was removed from Rotation X in Schedule Y in Project Z. Rotation X has been recalculated with the remaining participants. Please review the new set-up for Rotation X. It is recommended that you reach out the the current on-call responder to ensure continuity of on-call coverage.