Add Fixed_By in API for Packages Endpoint in V2

[TG1999]

          wrt. https://github.com/aboutcode-org/vulnerablecode/issues/1572#issuecomment-2475578554

... I think we need something a bit different.

We have this today:

    "packages": [
        {
            "purl": "pkg:pypi/[email protected]",
            "affected_by_vulnerabilities": [
                "VCID-486n-st7z-zqhz"
            ],
            "fixing_vulnerabilities": [],
            "next_non_vulnerable_version": "4.3",
            "latest_non_vulnerable_version": "5.2"
        }
    ]

Are we missing a "fixed by" that is just for a vulnerability-package?
May be something like that?

    "packages": [
        {
            "purl": "pkg:pypi/[email protected]",
            "affected_by_vulnerabilities": [
                {
                "vulnerability_id": "VCID-486n-st7z-zqhz",
                "fixed_by_package": "pkg:pypi/[email protected]",
                }
            ],
            "fixing_vulnerabilities": [],
            "next_non_vulnerable_package": "4.3",
            "latest_non_vulnerable_package": "5.2"
        }
    ]

with these definitions:

• fixed_by_package: a PURL for the first version that is fixing just one vulnerability
• next_non_vulnerable_package: a PURL for the first version that is non vulnerable to any vulnerability
• latest_non_vulnerable_package: a PURL for the latest version that is non vulnerable to any vulnerability

Question: would this reintroduce nesting?

Originally posted by @pombredanne in #1572 (comment)

[TG1999]

How does this look @pombredanne @tdruez