Resolves#36522: Icon mis-sized on KDE
Added new icon artifact to be used on KDE environments due to the fact
that previous icon appeared mis-sized on KDE envs.
For #25616
# Checklist for submitter
- [X] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/Committing-Changes.md#changes-files)
for more information.
- For Orbit and Fleet Desktop changes:
- [X] Manual QA must be performed in the three main OSs, macOS, Windows
and Linux.
- Tested on macOS, Windows, Ubuntu, Fedora (w/ and without system tray)
and Debian (w/ and without system tray)
## Details
This PR addresses the issue that on Ubuntu, if a user restarts their
display manager (e.g. with `sudo systemctl restart gdm3`), the Fleet
Desktop tray icon disappears and doesn't come back. The solution in this
PR is to add a function that runs in a loop and checks whether the tray
icon still exists, and if not, kills the Fleet Desktop process. The
parent Orbit process already has code to restart the desktop if it dies.
We also update the Orbit checker to run every 15 seconds, to limit the
delay in the icon coming back after a restart.
Also included in this PR is a rename from `desktop_unix.go` to
`desktop_linux.go`, which will be used automatically for linux builds,
and a new `desktop_darwin.go` for macos builds, and the removal of
redundant build directives for all.
