Download progress bar for nix-shell

[isolatedwebappdev]

Is your feature request related to a problem?

related: #1952 NixOS/nixpkgs#210663

Proposed solution

add download progress bar to nix shell or add flag for download progress bar

Alternative solutions

Additional context

Checklist

• checked latest Nix manual (source)
• checked open feature issues and pull requests for possible duplicates
• reviewed the contributing guide

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