Support for version inside extra-source?

[davesnx]

Hi, is it possible to support version (and maybe other variables) in extra-source.src?

extra-source "tailwindcss-linux-x64" {
  src: "https://github.com/davesnx/opam-tailwindcss/releases/download/%{version}%/tailwindcss-linux-x64"
  checksum: []
}

[kit-ty-kate]

This seems doable, however this would require either some sort of x-* field or to wait for opam 3.x, as this changes the expected syntax