UI update: Need warning when you change shared to specific runner

Repro steps:

1. Go to the Admin Area.
2. Go to the Runners page.
3. Click a shared runner to view its details.
4. In the Restrict projects for this runner section, to the right of a project, select Enable.

Actual result: The runner changes to a specific runner, and you cannot change it back to shared.

Expected result: A warning should tell the user that they are about to make a change they can't recover from. Something like: You are about to change this shared runner to a specific runner. Are you sure you want to continue?