Add compose functionality

What would you like to be added:

What do you think about adding a feature

bom compose 

for merging multiple SBOMs into a top level artefact?

A PoC already exists in sbom-composer, but as bom already supports wider range of functionalities, it would be great to have such option in order to work as all-in-one solution

Why is this needed:

Having granular SBOMs is not a new concept and it's inevitable to end-up operating with tens or hundreds of documents for many use-cases. By now this is only resolved by using External Document References, but it's much harder to work with linked documents, rather than a single composed one. Having the compose option would increase the usefulness of the bom tool, resolving this problem.

Bom already has parsing and filtering features to build compose on top of.