feat: Nix Shell support

[NickLarsenNZ]

Description

• Add nix-shell support
  • Removed superfluous copy/paste stuff from default.nix, and rearranged it to work more like the operators.
• Update niv dependencies (niv update)
• Update nix cargo dependencies (make regenerate-nix)
• Update OpenAPI Typescript schema

Important

Should we add niv update to the regenerate-nix Make target?
Also, should we add these nix dependency updates to the pre-commit hooks?

Definition of Done Checklist

• Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant
• Please make sure all these things are done and tick the boxes

Reviewer

Beta Give feedback

1. Code contains useful comments
2. (Integration-)Test cases added
3. Documentation added or updated
4. Changelog updated
5. Cargo.toml only contains references to git tags (not specific commits or branches)

Acceptance

Beta Give feedback

1. Feature Tracker has been updated
2. Proper release label has been added

[sbernauer]

This works perfectly fine, many thanks! (also tested make run-dev)