Import VEX data

It would be great to import VEX data when available to supplement the vulnerability and promote more efficient scoring and triage.

We have these issues to deal with the low level importers:
- https://github.com/nexB/vulnerablecode/issues/1122
- https://github.com/nexB/vulnerablecode/issues/1344
- https://github.com/nexB/vulnerablecode/issues/1345

There will likely either be some index of such documents that will emerge.

- @sethmlarson is specifically working on something for CPython https://sethmlarson.dev/security-developer-in-residence-weekly-report-19

- There is also related work in this area at https://github.com/anchore/grype/issues/1365