Use crontab rather than systemd for starting the camera up on boot

Why use a systemd module rather than using a crontab entry like this:

```
@reboot bash -c "export DISPLAY=:0; libcamera-hello -t 0 --autofocus-mode continuous"
```
I think that having a crontab script is easier than creating a systemd module.

Edit: seems like you want to load up the desktop before starting the camera.
Please refer to this link: https://forums.raspberrypi.com/viewtopic.php?t=294014