Add "Admin Contact Info" policy

[joshspicer]

Provide a way to encode contact information (url/email) where the admin configuring this policy can be reached.

There is precedent for this in other MDM solutions, for example tailscale.

This information is helpful for #239798 (comment), where you'd ideally want such an alert to provide actionable information.

cc/ @sandy081

[digitarald]

For GH-controlled settings, we could point them to the org page that the policy comes from.