add usecase where the name is just the image name in cdx/spdx sbom created via syft

[pxp928]

Signed-off-by: pxp928 parth.psu@gmail.com

1. Handle usecase where the "name" in CDX SBOM is just the image name (no registry or repo).
2. Update SPDX for single document name usecase
3. Update SPDX to partially match OCI spec until tool is SPDX element/relationships should be defined for the container image being described anchore/syft#1241 is resolved.
4. Updated setup.md with changes to query for SPDX

fixes #387

[pxp928]

This PR is will merge into heuristic-dev branch until use cases are captured.

[mlieberman85]

Handle usecase where the "name" in CDX SBOM is just the image name (no registry or repo).

Just a note that this isn't really a use case, it's just a part of both SPDX and CDX spec. It just so happens some tools include the repo, but nothing in the spec states that it must include repo. I would recommend we don't rely on the name at all too much.