Missing attribute preferred_cvss in the report json

[stonezdj]

What steps did you take and what happened:

Scan image in Harbor with trivy scanner

What did you expect to happen:
According the pluggable scaner spec
The CVE report should contain the preferred_cvss in the report json,

"preferred_cvss": {
             "score_v2": 5,
             "score_v3": 7.5,
             "vector_v2": "AV:N/AC:L/Au:N/C:N/I:N/A:P",
             "vector_v3": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
           },

Anything else you would like to add:

No

Environment:

• Harbor version: 2.8.0
• Harbor Scanner Adapter for Trivy version: v0.30.9
• Harbor installation process (Installer script, [Helm chart][harbor-helm], etc.):