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

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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

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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)