Fix issues with Fleet desktop periodically not appearing on macOS hosts

[ghernandez345]

Fleet version: Observed with the latest version of Fleet's agent (fleetd)

---

💥 Actual behavior

Fleet Desktop sometimes disappears from the menu bar on macOS hosts and doesn't come back unless the host is restarted.

We've seen this happen after a macOS update: #25689

🧑‍💻  Steps to reproduce

1. Install Fleet Desktop on a macOS host
2. Update macOS to a newer version
3. See that Fleet Desktop doesn't appear in the menu bar after macOS update (1-5% chance / reboot fixes)

Note - @lucasmrod was able to reproduce this issue (and verify the fix) here

🛠️ To fix

Update Fleet Desktop to be a launchd agent.

Flows that need to be checked

• DEP setup experience
• Host with previously installed desktop upgraded to new version
• Package / build / deploy to TUF questions
• Migration workflow
• Disk encryption

[georgekarrv]

Adding #19172