stacker-bom: a SBOM workflow tool/library for container image builds

Originally intended as a stacker companion tool to help with container image builds but anyone should be able to use it.

It uses https://github.com/kubernetes-sigs/bom and https://github.com/anchore/syft as its core BOM libraries.

Rationale

• Every component of a container image must be accounted for
• Source/build time tooling since most context is available at this time
• Easily integrate with stacker