[E2E] Delete a wiki page

What does this MR do?

This MR contains a test that creates a basic wiki with one page and tries to delete that page, verifying it by checking if the create a new page button is now visible which would indicate that there are no other pages currently available.

Closes gitlab-org/quality/testcases#268 (closed)

This MR also introduces a fix for a .vue file. It was using the old ok method of setting up the footer inside a modal. This was deprecated and a new way was recently introduced. This now allows QA to add its own selectors to a button and make testing a much nicer experience.