Cannot enable Wiki Page events from Webhook admin UI in a Project
Wiki Page events was introduced by !2998 (merged) as part of the work for #4233 While it has been added most to support the Slack service template, it lacked the UI components to enable it arbitrarily to any project.
Implementing that will help with #563 (closed).
We cannot close the issue yet, as the hook data we are sending is not 100% correct (we send details of the project, but should instead send details of the "ProjectWiki" attributes like URLs and repositories relative to the wiki itself, not the main project).