Extend Generic Findings Import to handle Mitigated Status, Mitigated Date

[paulOsinski]

I want to be able to import Generic Findings that are already Mitigated, with their Mitigation Date stored in DefectDojo.

For example:

{
  "findings": [
    {
      "title": "test title",
      "description": "description",
      "active": false,
      "verified": false,
      "mitigated": "2021-01-30",
      "is_mitigated": true,
      "severity": "Medium",
      "impact": "Some impact",
      "date": "2021-01-06",
      "cve": "CVE-2020-36234",
      "cwe": 261,
      "cvssv3": "CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N",
      "tags": [
        "security",
        "network"
      ],
      "unique_id_from_tool": "3287f2d0-554f-491b-8516-3c349ead8ee5",
      "vuln_id_from_tool": "TEST1"
    }
  ]
}

Should create a Finding with a status of Closed and a Mitigation Date of 2021-01-30, regardless of when I import the file. Use of the dateutil parser would be best here. Please update the documentation as part of these efforts