Include packages in application SBOM

[nscuro]

By using go list, we get to know which packages are actually used, but we currently don't include this information in the SBOM.

Using the info we already have, we can construct a structure according to modules > packages > files, for example:

{
    "bom-ref": "pkg:golang/github.com/ProtonMail/go-crypto@v0.0.0-20210428141323-04723f9f07d7",
    "type": "library",
    "name": "github.com/ProtonMail/go-crypto",
    "version": "v0.0.0-20210428141323-04723f9f07d7",
    "scope": "required",
    "hashes": [
        {
            "alg": "SHA-256",
            "content": "62825b7a72bd0baed29339037e642e5659f4e328078f7be365f77d14bf869904"
        }
    ],
    "purl": "pkg:golang/github.com/ProtonMail/go-crypto@v0.0.0-20210428141323-04723f9f07d7",
    "components": [
        {
            "bom-ref": "pkg:golang/github.com/ProtonMail/go-crypto#bitcurves@v0.0.0-20210428141323-04723f9f07d7",
            "type": "library",
            "name": "bitcurves",
            "version": "v0.0.0-20210428141323-04723f9f07d7",
            "scope": "required",
            "purl": "pkg:golang/github.com/ProtonMail/go-crypto#bitcurves@v0.0.0-20210428141323-04723f9f07d7",
            "components": [
                {
                    "type": "file",
                    "name": "bitcurve.go",
                    "version": "v0.0.0-2472c8e5f796",
                    "scope": "required",
                    "hashes": [
                        {
                            "alg": "MD5",
                            "content": "b4689d8871aa46bb387ef148944f8da8"
                        },
                        {
                            "alg": "SHA-1",
                            "content": "2472c8e5f796d8463738938fea98398dabba08ad"
                        }
                        // ...
                    ]
                }
            ]
        }
    ]
}

Including the packages should probably be enabled per default, but including individual files should still be optional.