Docs for conflict-related status messages

In #281171 (closed), we are developing different status messages when a merge request has one of these conflict types:

• Modified in both the source and target branch
• Modified in source, removed in target
• Removed in source, modified in target
• Renamed differently in both the source and target branches
• Removed in source, renamed in target
• Renamed in source, removed in target
• Created in both the source and target branch

To follow the pattern we are slowly establishing for status messages, these should contain three parts:

[Current status]: explanation of issue [link to next step]

As part of the discussion, @patrickbajao / @pedroms / @sunjungp identified the lack of a single location we could link to. We have a couple of different pages that touch on conflict resolution in merge requests, but we've never really considered where this information should live, and we also don't have 1:1 matches with the messages we'll be displaying.

Current pages:

• https://docs.gitlab.com/ee/topics/git/git_rebase.html#merge-conflicts
• https://docs.gitlab.com/ee/user/project/merge_requests/resolve_conflicts.html

At heart, this will become a question of whether the information should live with merge requests, or with the Git topics.

Related issues

• Related to #281171 (closed) where the need for this issue was uncovered.