Do not subscribe to issue when impacting related MR

Proposal

In some situations we subscribe a user to an MR or other item when an action they take impacts that. An example situation is:

1. User A Opens an MR with a "Merge after pipeline succeeds" Set.
2. The pipeline takes a while but is in progress
3. User B force merges another MR that causes the initial MR to have to stop
4. User B is subscribed to the MR User A opened.

While it would be important to notify User A why their MR cannot be merged anymore it doesn't seen necessary to subscribe User B to the MR. A notification will appear on User A's MR that the pipeline was aborted. This tags User B and likely why the subscribe is happening.

User B does not need to be subscribed from a functional stand point it seems, and removing; or providing the option of this, seems a good addition.

label groupcode review