New invocation mode: Decode and print RPKI file in standard output

Orders from above. Something like
$ fort --mode=print cache/a.b/rpp1/achoo.roa
{
    "ContentType": "signedData",
    "SignedData": {
        "version": 3,
        "digestAlgorithms": [
            {
                "algorithm": "sha256"
            }
        ],
        "encapContentInfo": {
            "ContentType": "ROA",
            "RouteOriginAttestation": {
                "asId": 1234,
                "ipAddrBlocks": [
                    {
                        "addressFamily": "IPv4",
                        "addresses": [
                            {
                                "prefix": "192.0.2.1",
                                "length": 24,
                                "maxLength": 26
                            }
                        ]
                    },
                    {
                        "addressFamily": "IPv6",
                        "addresses": [
                            {
                                "prefix": "2001:db8::1",
                                "length": 29,
                                "maxLength": 48
                            }
                        ]
                    }
                ]
            }
        },
        "certificates": [
            {
                "tbsCertificate": {
                    "version": 2,
                    "serialNumber": "0123456",
                    "signature": "sha256WithRSAEncryption",
                    "issuer": {
                        "commonName": "aabbccddeeff"
                    },
                    "validity": {
                        "notBefore": "2024-01-01 00:00:00Z",
                        "notAfter": "2025-07-01 00:00:00Z"
                    },
                    "subject": {
                        "commonName": "001122334455"
                    },
                    "subjectPublicKeyInfo": {
                        "algorithm": "rsaEncryption",
                        "subjectPublicKey": "---BEGIN PUBLIC KEY---blah blah---END PUBLIC KEY---\n"
                    },
                    "issuerUniqueID": null,
                    "subjectUniqueID": null,
                    "extensions": {
                        "X509v3 Subject Key Identifier": {
                            "critical": false,
                            "value": "abcdef"
                        },
                        "X509v3 Authority Key Identifier": {
                            "critical": false,
                            "value": "56789"
                        },
                        "X509v3 Key Usage": {
                            "critical": true,
                            "value": "Digital Signature"
                        },
                        "Authority Information Access": {
                            "critical": false,
                            "value": "rsync://a.b.c/d/e.cer"
                        },
                        "Subject Information Access": {
                            "critical": false,
                            "value": "rsync://a.b.c/d/f.roa"
                        },
                        "X509v3 CRL Distribution Points": {
                            "critical": false,
                            "value": "rsync://a.b.c/d/g.crl"
                        },
                        "X509v3 Certificate Policies": {
                            "critical": true,
                            "value": "ipAddr-asNumber"
                        },
                        "sbgp-ipAddrBlock": {
                            "critical": true,
                            "value": "192.0.2.1/24"
                        }
                    }
                },
                "signatureAlgorithm": "sha256WithRSAEncryption",
                "signatureValue": "blah blah blah"
            }
        ],
        "signerInfos": [
            {
                "version": 3,
                "sid": "1234",
                "digestAlgorithm": {
                    "algorithm": "sha256"
                },
                "signedAttrs": {
                    "Content-Type": [
                        "ROA"
                    ],
                    "Signing-Time": [
                        "2024-01-01 00:00:00Z"
                    ],
                    "Message-Digest": [
                        "aaabbbccc"
                    ]
                },
                "signatureAlgorithm": {
                    "algorithm": "sha256WithRSAEncryption",
                    "parameters": "0500"
                },
                "signature": "blah blah blah"
            }
        ]
    }
}
NICMx / FORT-validator

New invocation mode: Decode and print RPKI file in standard output #122
