Upstream to nixpkgs

[srid]

As a final step of #140, let's upstream to nixpkgs:

Preliminary

• Finalize LICENSE for omnix and crates @srid
• Release omnix crate to crates.io @srid

Second version

• Stop using nix fork Use inspect to remove the dependency on nix fork for flake-schemas #277
• om init: Prepare for wider use #282
• Rename nixci and nix_health crates for consistency
• Release to crates.io

Upstream

• Upstream pkgs.omnix to nixpkgs
  • Check: it installs the om binary (not omnix-cli).
  • Check: auto completion works on zsh (macOS) and bash (Linux)
  • Check: it builds on Intel mac
    • Even if upstream doesn't test x86_64-darwin in CI, we should manually make sure that our PR builds.

[srid]

All crates have now been published:

https://crates.io/crates/omnix-cli

[srid]

Now that we no longer depend on the Nix fork, I'll work on preparing for release: