Import/Export to SPDX documents

[kestewart]

It would be very useful if grafeas could consume and generate SPDX documents (https://spdx.github.io/spdx-spec/) to enable sharing of information with other open source software bill of materials generation and scanning tools available, like TERN, FOSSology, Scancode.

Describe the solution you'd like
Please add option to enable grafeas to export and import SBoM document information from one of the valid and planned SPDX formats (tag:value, rdfa, xml, json, yaml).
There are libraries available to support subsets of these format in python and go are available in https://github.com/spdx

The SPDX project has some GSoC students working on improving some of the capabilities of the libraries over the summer so fall timeframe is a good window to deep dive on this is in file.