Fix "Confirm user" button on tabs other than "Account" and "SSH keys" in admin area

📖 What does this MR do?

Related to #335900 (closed)

In !64812 (merged) we moved the Confirm user button to the header which made it available on all the tabs. Due to some missing JavaScript and a JavaScript error the Confirm user currently only works on the Account and SSH keys tabs. This MR adds the missing JavaScript, fixes the error that was causing issues, and refactors some JavaScript in the process.

💻 Local testing

1. Login as an Admin (root user in GDK)
2. Navigate to Menu -> Admin -> Users and note the username of one of the users
3. In your terminal in the gdk/gitlab directory run bin/rails console
4. Run the following commands
   • user = User.find_by_username('<user name>')
   • user.confirmed_at = nil
   • user.save
5. Navigate to Menu -> Admin -> Users and choose that user
6. The Confirm user button should work in all of the tabs

📹 Videos

Before	After
Screen_Recording_2021-07-12_at_1.23.57_PM720p	Screen_Recording_2021-07-12_at_1.22.54_PM720p

🚦 Does this MR meet the acceptance criteria?

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