respect allRefs=1 when using nix flake prefetch

[figsoda]

Motivation

So out of tree revisions can be fetched with nix flake prefetch by using allRefs=1 as a query parameter

Context

Makes it possible to work around #5128 when using nix flake prefetch

Here is an example that works after this change:

nix flake prefetch --extra-experimental-features "nix-command flakes" git+https://github.com/fdehau/tui-rs?allRefs=1&rev=6f4831a769d7adead8c53986cc2255e61c283e70

Checklist for maintainers

Maintainers: tick if completed or explain if not relevant

• agreed on idea
• agreed on implementation strategy
• tests, as appropriate
  • functional tests - tests/**.sh
  • unit tests - src/*/tests
  • integration tests - tests/nixos/*
• documentation in the manual
• code and comments are self-explanatory
• commit message explains why the change was made
• new feature or incompatible change: updated release notes

Priorities

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