[gpu-configurator] Add new flag on setting nvidia kernel driver

```
🐚 Executing finalizer on / /bin/bash [-c gpu-configurator nvidia kernel --proprietary=false 560.35.03 6.1.109-macaroni || true]
💣 link /lib/modules/nvidia-open/560.35.03/6.1.109-macaroni/video/nvidia.ko.zst /lib/modules/6.1.109-macaroni/video/nvidia.ko.zst: file exists 🔥
```
In order to avoid this message when another driver is configured we can add a flag `--if-not-exists` or similar.

Start by locating the gpu-configurator nvidia kernel command and the code handling the driver-link operation. Check how command-line flags are parsed, then verify that the proposed flag avoids the file-exists message when another driver is already configured while preserving the existing behavior otherwise.

Written by the indexing model from the issue text.