feat(wkg,core,client): intial wkg workspace approach

[mkatychev]

PR adds initial workspace support for wkg fetch and wkg publish

wkg publish:

• added --workspace flag to select packages for publishing from the wkg.toml manifest (if workspace table is present)
• added --skip-dupes: to allow idempotent publishing, wkg publish will skip publishing a version that is already available upstream instead of producing an error.

wkg fetch:

• supports multi package lockfiles by unioning the dependency trees of all included packages
• supports workspace fetching

Introduced WorkspaceConfig to manage workspace configurations in manifests:

wasm-pkg-tools/crates/wasm-pkg-core/src/manifest/workspace.rs

Lines 11 to 20 in 0616061

	pub enum WorkspaceConfig {
	// `[workspace]`
	Root(WorkspaceRootConfig),
	// - `workspace = "path/to/workspace/root"`
	// - TODO(mkatychev): implement workspace package level field
	// - https://doc.rust-lang.org/cargo/reference/manifest.html#the-workspace-field
	// Member {
	// root: Option<String>,
	// },
	}

WorkspaceRootConfig added as a virtual-manifest stand-in:

wasm-pkg-tools/crates/wasm-pkg-core/src/manifest/workspace.rs

Lines 48 to 53 in 0616061

	pub struct WorkspaceRootConfig {
	#[serde(default, skip)]
	pub(super) root_dir: PathBuf,
	pub members: Vec<PathBuf>,
	pub metadata: Option<Metadata>,
	}

[vados-cosmonic]

LGTM 🚀

Mostly nits, and feel free to push any you want to followup(s)!