Get vulnerability severity

[dloez]

We need to retrieve the level of each vulnerability from OSV, this should be done in the collect_vulnerabilities Huey task.
Also, calculate the number of each vulnerability levels and the total so we can serve that data without needing to recalculate it once again for each serve.

[dloez]

This is more complex that I first thought, this is an example of the severity returned by OSV of a vulnerability:

"severity": [
    {
        "type": "CVSS_V3",
        "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H"
    }
]

OSV returns a CVSS_VX string, we need to store that severity and, for the moment, calculate its average score and a string representation.
More information can be found here.