Shard merge_request_diff_commit_users
## Context
`merge_request_diff_commit_users` holds a name/email for both author and committer of a given MergeRequestDiffCommit, as they are not guaranteed to be a previously recognized/registered User. This leads to duplication with User records, but these authors/committers could exist across many projects and organizations, which is why we initially left this table as clusterwide.
## Proposal
Our plan for sharding this table is this:
1. ~~https://gitlab.com/gitlab-org/gitlab/-/issues/517131+~~
2. ~~https://gitlab.com/gitlab-org/gitlab/-/issues/517132+~~
3. ~~https://gitlab.com/gitlab-org/gitlab/-/issues/536253+~~
4. ~~https://gitlab.com/gitlab-org/gitlab/-/issues/517133+~~
5. ~~https://gitlab.com/gitlab-org/gitlab/-/issues/517134+~~
6. ~~https://gitlab.com/gitlab-org/gitlab/-/issues/526298+~~
7. ~~https://gitlab.com/gitlab-org/gitlab/-/issues/517135+~~
8. ~~https://gitlab.com/gitlab-org/gitlab/-/issues/548144+~~
9. ~~https://gitlab.com/gitlab-org/gitlab/-/issues/526725+~~
## Current status
```glql
title: ⏳ Work in progress/up next (assigned + milestone)
display: table
sort: milestone asc
fields: state, milestone, assignee, title, labels("workflow::*"), lastComment
query:
group = "gitlab-org" and epic = &16677
and state = opened and assignee != None and milestone != None
```
```glql
title: 🎉 Done
display: table
sort: closedAt desc
fields: state, closedAt, milestone, assignee, title
query:
group = "gitlab-org" and epic = &16677
and state = closed
```
epic