In order for the installer to restart the GUI correctly post-upgrade, we
need the GUI to be able to register its restart preferences.
This PR adds API support for doing so. I'm adding it to OSS so that it
is available should we need to do any such registrations on OSS binaries
in the future.
Updates https://github.com/tailscale/corp/issues/13998
Signed-off-by: Aaron Klotz <aaron@tailscale.com>