Disable nix tooling

[gngram]

Description of changes

• Disables nix tooling if development setup is not enabled
  - Indirectly disables nix tooling in release build
• Enables automatic garbaze collection in ghaf-host and disable everywhere else.
• Fixes:
  https://jira.tii.ae/browse/SSRCSP-3457

Checklist for things done

• Summary of the proposed changes in the PR description
• More detailed description in the commit message(s)
• Commits are squashed into relevant entities - avoid a lot of minimal dev time commits in the PR
• 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:
  • Tested on Lenovo X1 x86_64
  • Tested on Jetson Orin NX or AGX aarch64
  • Tested on Polarfire riscv64
• Author has run make-checks and it passes
• All automatic Github Action checks pass - see actions
• Author has added reviewers and removed PR draft status
• Change requires full re-installation
• Change can be updated with nixos-rebuild ... switch

Instructions for Testing

• List all targets that this applies to:
  • Lenovo X1
  • Jetson Orin NX and AGX
• Is this a new feature
  • List the test steps to verify:
    • In release build, no nix commands should be available, nix daemon should not be running
    • In debug build nix daemon should be running in all VMs and automatic garbaze collection should be available only in host.
    • If automatic garbaze collection is enabled 'systemctl list-timers' should list 'nix-gc' also
• If it is an improvement how does it impact existing functionality?

[brianmcgillion]

grabage?

[humaidq-tii]

Maybe better to avoid using mkForce, set these options above? So nix.enable = cfg.enable