chore: add restartsec to systemd service file

[Sped0n]

Some linux distro(like suse) would complain if user set Restart=always, but have not included any StartLimitIntervalSec, StartLimitBurst, or RestartSec directives to prevent the service from entering an infinite Start request repeated too quickly loop

luna:~ # systemctl status beszel-hub
× beszel-hub.service - Beszel Hub Service
     Loaded: loaded (/etc/systemd/system/beszel-hub.service; enabled; preset: disabled)
     Active: failed (Result: start-limit-hit) since Tue 2024-12-03 21:35:01 CST; 2s ago
   Duration: 42ms
    Process: 13519 ExecStart=/opt/beszel/beszel serve --http 0.0.0.0:10002 (code=exited, status=0/SUCCESS)
   Main PID: 13519 (code=exited, status=0/SUCCESS)
        CPU: 18ms

Dec 03 21:35:01 luna systemd[1]: beszel-hub.service: Scheduled restart job, restart counter is at 5.
Dec 03 21:35:01 luna systemd[1]: beszel-hub.service: Start request repeated too quickly.
Dec 03 21:35:01 luna systemd[1]: beszel-hub.service: Failed with result 'start-limit-hit'.
Dec 03 21:35:01 luna systemd[1]: Failed to start Beszel Hub Service.

[henrygd]

Merged, thanks 👍