[FEATURE]: Add KEV information to vulnerablity

[mtausig]

Describe the feature

The schema should be expanded so that the Vulnerability type can include information if the vulnerability has been included on a KEV (Known Exploited Vulnerability) list as provided by CISA or ENISA.

Possible solutions

Should contain the following properties:

• KEV Provider
• Date of retrieval
• Boolean flag for inclusion on list
• Date when vulnerability was added to the list

Alternatives

None

Additional context

Has already been discussed here: #481 (comment)

[stevespringett]

Related to #481