GraphQL: Create any remaining Issue mutations needed for sidebars

We need to create any remaining mutations on Issues needed to support the sidebar.

Needed for #17589 (closed)

1. #36307 (closed) : Assignee(s) of the issue - taking into account that multiple assignees are Starter+.
2. #36309 (closed) : Epic.
3. #36312 (closed) : Milestone (see also #5135 (closed)).
4. #36313 (closed) : Due date.
5. #36316 (closed) : Labels (see !19642 (merged) for this for epics and !19913 (merged) for merge requests).
6. #36317 (closed) : Weight.
7. #36318 (closed) : Confidential status.
8. #36319 (closed) : Locked status. (see !19913 (merged) for merge requests)
9. #36321 (closed) : Subscribed status. (see !19913 (merged) for merge requests)
10. #36322 (closed) : Move issue.
11. #36323 (closed) : Todo add / mark as done. (see also see also !18581 (merged))