Add KEV information to v6 DB

[wagoodman]

This PR adds the CISA KEV data shape to the DB as a new table and plumbs through VulnerabilityMetadata calls to attach matching KEV entries for a given vulnerability.

This adds a new vulnerability.knownExploited[] array to the JSON output:

$ grype 'cpe:2.3:a:zohocorp:manageengine_desktop_central:1' -o json | jq '.matches[] | select(.vulnerability.id == "CVE-2020-10189").vulnerability.knownExploited'
 ✔ Scanned for vulnerabilities     [0 vulnerability matches]  
   ├── by severity: 10 critical, 10 high, 5 medium, 0 low, 0 negligible
   └── by status:   19 fixed, 6 not-fixed, 0 ignored 

[
  {
    "cve": "CVE-2020-10189",
    "vendorProject": "Zoho",
    "product": "ManageEngine",
    "dateAdded": "2021-11-03",
    "requiredAction": "Apply updates per vendor instructions.",
    "dueDate": "2022-05-03",
    "knownRansomwareCampaignUse": "unknown",
    "urls": [
      "https://nvd.nist.gov/vuln/detail/CVE-2020-10189"
    ],
    "cwes": [
      "CWE-502"
    ]
  }
]

I've removed the KEV vulnerabilityName and shortDescription from the DB and grype output as it is redundant to the NVD data; here's the removed values for the above record as an example:

{
  "vulnerabilityName": "Zoho ManageEngine Desktop Central File Upload Vulnerability",
  "shortDescription": "Zoho ManageEngine Desktop Central contains a file upload vulnerability that allows for unauthenticated remote code execution."
}

Partially addresses #1511