How should GitLab note updates be handled?

Nobody has claimed this yet.

GitLab has a webhook for notes "updates", i.e. when a comment in an MR or issue is edited. Currently the code doesn't make a difference when it receives a note update or a note creation, so it appears as a new comment which seems wrong.

Logically, we should use a replacement relation to edit the first message. Firstly, that would mean that we need to keep track of the event ID for every note. Secondly, given that MR review comments are batched, it becomes a bit more complicated to construct the edit. We would need to keep track of _every_ note that was sent in an event, and probably require to fetch the other notes in the event to have the full edit content.

We could also choose the easy way out and ignore edits.

No files, tests, or entry points are named. Start by locating the GitLab webhook handling for note creation and note updates, then determine whether edits should use replacement relations or be ignored; done requires an agreed behavior for edited notes and coverage for that decision.

Written by the indexing model from the issue text.