For #25924
This PR attempts to fix the issue where the Fleet desktop icon sometimes
fails to appear on MacOS hosts until the hosts are rebooted. Anecdotal
evidence points to this being an issue when system setup is happening,
leading to the theory that Orbit is attempting to launch the app as
`_mbsetupuser` rather than the real logged-in user. The fix here is to
use a different command to get the name of the logged-in user (ignoring
`_mbsetupuser` if it appears), and to launch the desktop app as that
user using `sudo`.
I have tested this on MacOS and Ubuntu hosts, and verified that the
desktop app launches as expected on both.
We don't have a solid reproduction scenario for the issue, but we do
have [some ways to look for relevant
errors](https://github.com/fleetdm/fleet/issues/19172#issuecomment-2627812786),
so we can try this out and see if those errors cease.
> 📜 Related issue: https://github.com/fleetdm/fleet/issues/14698
# Checklist for submitter
If some of the following don't apply, delete the relevant line.
<!-- Note that API documentation changes are now addressed by the
product design team. -->
- [x] Changes file added for user-visible changes in `changes/` or
`orbit/changes/`.
See [Changes
files](https://fleetdm.com/docs/contributing/committing-changes#changes-files)
for more information.
- [x] Manual QA for all new/changed functionality
- For Orbit and Fleet Desktop changes:
- [x] Manual QA must be performed in the three main OSs, macOS, Windows
and Linux.
- [x] Auto-update manual QA, from released version of component to new
version (see [tools/tuf/test](../tools/tuf/test/README.md)).
