Add types in reference URLs

[Hritik14]

Context

Many vulnerability database designs have a support for types of given reference URLs. For eg:

NVD

Schema:

• https://github.com/CVEProject/cve-schema/blob/master/schema/v5.0/CVE_JSON_5.0_schema.json
• https://github.com/CVEProject/cve-schema/blob/master/schema/v5.0/tags/reference-tags.json

OSV

https://ossf.github.io/osv-schema/#references-field

Proposal

Having the type of reference might help in future to filter out the patches and exploits from other references.
It is not sure that we want to restrict our reference types to a few choices as done by OSV and NVD.
Further, we are not inferring the type of reference by our own but trust the upstream.

Thus, we are considering having a JSONField with contents like nvd:customer-entitlement, osv:fix, osv:web for reference type.
It is a JSONField and not a postgres Array because Arrays are specific to postgres but JSONFields are available in other dbs as well.

(via: https://github.com/nexB/vulnerablecode/wiki/WeeklyMeetings#meeting-on-tuesday-2022-04-26-at-1000-utc)