Update epic issue when an issue is moved

When moving an issue it updates related epic issue reference, so the new issue is referenced from the epic instead of the old issue.

This is EE only feature, it adds a CE vs EE difference into app/services/issues/move_service.rb which is not ideal. An alternative would be to keep rewrite_epic_issue method in CE empty and override it in EE ee/app/services/ee/issues/move_service.rb but it wouldn't be better because it would add an empty EE specific method into CE anyway.

Related to gitlab-ce#41949