Registry tooling and wac

[macovedj]

Added instructions for tools that have registry support, (cargo-component, wit, and wac). The tools that have registry support have a few different assumptions about how both WIT packages and components are referenced, so I had to change some of the existing examples a bit.

That being said I'm not sure if we want to continue to encourage users to perform composition using some of the old flows anymore (wasm-compose may end up being replaced by wac, in which case UI based composition may look a bit different?).

I figure these changes are a good starting point for a discussion about these topics, which may lead to more changes in the examples. Also opening as a draft as there are some pending code changes that will be needed in order for users to have multiple namespaces in their compositions... namely https://github.com/bytecodealliance/cargo-component/pull/275, https://github.com/bytecodealliance/wac/pull/91, https://github.com/bytecodealliance/registry/pull/263. The docs should probably not be updated until these get merged.