Add package publish

[THenry14]

This PR adds a support for publishing packages to a registry.
In order to succesfully upload a package one needs to provide an authentication token via SCARB_AUTH_TOKEN env variable.

sncast_std $ cargo run --manifest-path /path/to/scarb/Cargo.toml --bin scarb -- publish --index http://localhost:8000/ 
   Packaging sncast_std v0.30.0 (/(...)/sncast_std/Scarb.toml)
   Verifying sncast_std-0.30.0.tar.zst
   Compiling sncast_std v0.30.0 (/(...)/sncast_std/target/package/sncast_std-0.30.0/Scarb.toml)
    Finished release target(s) in 33 seconds
    Packaged 7 files, 14.10 KiB (3.71 KiB compressed)
   Uploading sncast_std v0.30.0 (registry+http://localhost:8000/)
   Published sncast_std v0.30.0 (registry+http://localhost:8000/)

[mkaput]

lgtm from my side, though I didn't review this carefully (only picked stuff that interested me)