Allow setting Prek's Environment Variables declaratively

[ilovelinux]

Use-case

• I have some local Rust hooks.
• Those Rust hooks uses:
  • clippy
  • rustfmt

but:

• Those tools are available with rustup profile default or complete.
  • PREK_RUSTUP_PROFILE=default is needed when running the hooks for the first time.

Problem

There's no way to declaratively add clippy and rustfmt as dependencies since:

• additional_dependencies doesn't support installing components.
• PREK_RUSTUP_PROFILE=default can't be set declaratively.