Wiki events should be created by git-access pushes

Problem to solve

Wiki events should be created by pushes to wiki repos

Intended users

Any user who edits a wiki locally and pushes changes with Git.

Further details

This is aimed at making user contributions more visible, supporting all preferred workflows.

Proposal

This adds behavior into the post-push event handler that records changes for all edited (created/modified or deleted) wiki pages.

Documentation

This does not require any user changes.

Feature flags

This feature is guarded behind the :wiki_events_on_git_push feature flag

Availability & Testing

Tests are needed that simulate the behavior of editing a wiki using the git-access protocol.

What does success look like, and how can we measure that?

A user's contributions will be visible on the project activity stream following a git push to the wiki.