Add confirmation sent at section to admin users view

What does this MR do and why?

In order to help with support tickets when it comes to email confirmations, this MR adds a Email verification last sent at section to the admin users view:

No verification email sent	Email sent

How to set up and validate locally

1. Go to Admin Area -> Users.
2. Click on the Administrator user, or find the user you are logged in as and click on it.
3. Verify that the Email verification last sent at section is shown, and that the date is never.
4. In the sidebar, click on the user avatar to show the dropdown menu, then select Edit profile.
5. Find the Email input box, and change it to something else. Click on Update profile settings at the bottom.
6. Go back to the Administrator user details page. Verify that the Email verification last sent at section now shows a date.

Related to https://gitlab.com/gitlab-org/modelops/anti-abuse/team-tasks/-/issues/589