Add a Chainguard Images container SBOM and associated test

[jspeed-meyers]

Add a Chainguard Images SBOM and an associated test

[Full disclosure: I work at Chainguard. The Chainguard engineering team uses ntia-conformance-checker to check the conformance of some Chainguard Images SBOMs with the NTIA minimum elements. Adding in this test (A) doesn't hurt! and (B) ensures that any future breaking changes related to Chainguard Images SBOM will be flagged early.]