[Feature Request]: Set hostname with automatic first boot config

### Which feature would you like to have?

I am about to setup a cluster of SBCs with Armbian and read about "Automatic first boot configuation": https://docs.armbian.com/User-Guide_Autoconfig/

I thought it would be great to be able to set the desired hostname from this config too, e.g. `PRESET_HOSTNAME` directive.

I have found that it's done in `armbian-firstlogin` script [here](https://github.com/armbian/build/blob/main/packages/bsp/common/usr/lib/armbian/armbian-firstlogin). I am happy to help if you think this is a feature worth implementing, with some guidance I could make a PR for it.

### Funding

- [ ] [I am willing to cover expenses](https://www.armbian.com/contact/)