dev.knotless.assignItem

As `knotless pull assign`, `unassign`, `ask-review` and `unask-review` do: the repository's owner and collaborators rewrite their dev.knotless.assignment record about it, and a pull's author asks for reviews in the pull itself. A pull's author stops asking only those it asked, and a maintainer only those maintainers asked. Requires the session cookie the pages' login sets.