Support git dependencies for package_metadata

[darkrift]

rules_rs doesn't yet support git dependencies.

rules_rs/rs/rust_crate.bzl

Line 40 in 6848d1a

# TODO(zbarsky): repository url for git deps?

The cyclonedx reference app for cargo dependencies is https://github.com/CycloneDX/cyclonedx-rust-cargo which generates the following purl for the git_crates test project : test.cdx.json

{
      "type": "library",
      "bom-ref": "git+https://github.com/cloudflare/wirefilter#wirefilter-engine@0.7.0",
      "author": "Ingvar Stepanyan <me@rreverser.com>",
      "name": "wirefilter-engine",
      "version": "0.7.0",
      "description": "An execution engine for Wireshark-like filters",
      "scope": "required",
      "licenses": [
        {
          "expression": "MIT"
        }
      ],
      "purl": "pkg:cargo/wirefilter-engine@0.7.0?vcs_url=git%2Bhttps://github.com/cloudflare/wirefilter%40bcc69c10741ca80dbb16751bd7e597f89c23015d",
      "externalReferences": [
        {
          "type": "vcs",
          "url": "https://github.com/cloudflare/wirefilter"
        }
      ]
    },

For PURL common qualifiers, see :

https://github.com/package-url/purl-spec/blob/main/docs/common-qualifiers.md