Hide the runner registration token from the screen

Problem

When we visit the runner's admin page we immediately see the runner's registration token.

This means we can't easily take screenshots or share videos of the UI (or have eavesdroppers) when using this page.

Proposed Solution

Show a masked version of the token initially, have a "click to reveal" to show the content of the token, for example:

Customer

The grouprunner team can more easily show demos of the project without fear of disclosing information.