Add SBOM output pipeline(s) or output file options

[mjherzog]

ScanCode Toolkit currently offers SPDX output files. You can currently create an SBOM output by downloading the standard SCIO JSON output and running it through SCTK on your local machine. It would be useful to have SBOM output as an option directly from SCIO. In the near term, we could add pipelines that include the SBOM creation step. Longer term, it would be better to add this as an output file option to avoid duplicating pipelines just to offer SBOM output.