x1-installer: add checks in installer script, other improvements

[humaidq-tii]

The image path is now set as an environment variable, so the script derivation could be reused. Also the installer derivation is created using writeShellApplication which will test against shellcheck.

Also added message on running the installer. The installer now only shows devices and the vendor/name, and doesn't include the partitions.

The installer also has proper confirmation prompts, and also warn the user if they are trying to install Ghaf on a removable device.

Description of changes

• Use writeShellApplication for installer, specify runtimeInputs. Now script is always checked against shellcheck.
• Installer improvements
  • Lists only actual devices, while partitions and loop devices are not shown. This uses hwinfo package.
  • Includes vendor and disk name of each drive (e.g. Sandisk Cruzer Force).
  • Installer verifies device user input, whether the device actually is valid.
  • Additionally confirms if the user is trying to install Ghaf on removable media.
  • Proper [y/N] prompts for each of the confirmations.
  • Shows error if not executed as root.
  • Image path given as environment variable, means the shell script doesn't have to always be rebuilt with disko image.
• Changed hostname to be ghaf-installer.
• Added getty help message on running ghaf-installer.

Checklist for things done

• [x] Summary of the proposed changes in the PR description
• [x] More detailed description in the commit message(s)
• [x] Commits are squashed into relevant entities - avoid a lot of minimal dev time commits in the PR
• [x] Contribution guidelines followed
• [ ] Ghaf documentation updated with the commit - https://tiiuae.github.io/ghaf/
• [ ] PR linked to architecture documentation and requirement(s) (ticket id)
• [ ] Test procedure described (or includes tests). Select one or more:
  • [x] Tested on Lenovo X1 x86_64
  • [ ] Tested on Jetson Orin NX or AGX aarch64
  • [ ] Tested on Polarfire riscv64
• [ ] Author has run nix flake check --accept-flake-config and it passes
• [ ] All automatic Github Action checks pass - see actions
• [x] Author has added reviewers and removed PR draft status

Testing

• Build the installer image
• Boot the live cd
  • There should be a message on boot with instructions to run the installer.
  • Run installer, should get list of actual devices (no partitions).
  • Input invalid device name, or specify a device partition, should give an error device doesn't exist and prompt again.
  • Input valid device, confirm, should install properly.

[milva-unikie]

Tested on Lenovo-X1 installer (nix build github:humaidq-tii/ghaf/better-installer#lenovo-x1-carbon-gen11-debug-installer)

I was able to follow the testing steps and everything is working.

• Installer image boots
• Error message shown when not running installer with sudo
• Devices are shown correctly
• Error message shown when device name is invalid
• Installation works and Ghaf boots after
• Test-automation passes on installed image