Update the Admin Audit Events sorting dropdown to a Vue app which utilises GitLab UI components

Problem to solve

The current Admin Audit Events sorting field is a HAML field which is tied to the backend response and is not using GitLab UI's components to render.

Proposal

As part of the work to improve the user experience for the Admin Audit Events page we should update the sorting dropdown to a Vue app. This will allow us to use GitLab UI fully, make it easier to transition to using a new Audit Events API and contribute to merging the page into a single Vue App rather than keeping them separated.