Unified publishing

[lann]

Currently, if you want to publish a package to a warg registry you use warg and if you want to publish to an OCI registry you use some OCI tool (like oras). For toolchain-specific tools like cargo-component that want to support their own publish flow it would be nice to have a unified publishing library available.

Supporting the full feature set of e.g. warg seems out of scope for this library, but it does seem plausible to support a subset of common operations like basic single release publishing, selecting the appropriate protocol by consulting the well-known wasm-pkg URL for the destination registry domain.

This functionality could also be exposed via an e.g. wkg publish subcommand.

[thomastaylor312]

This should be completed in #80