Normalize Windows CertLog Certificates output

[JSCU-CNI]

PR #1415 introduced a helper function to parse X509 certificates. The function certlog.certificates introduced in #1443 performs it's own rudimentary certificate parsing. Ideally the output of this function should contain normalized fields (e.g. serial_number as varint, issuer_dn, etc.).

[william-billaud]

regarding common fields, after a quick look here are my results.

WebserverCertificateRecord name	WebserverCertificateRecord type	Certlog CertificatRecord Name	Certlog CertificatRecord type
fingerprint	digest	CertificateHash2	N/A
serial_number	varint	serial_number	string (0x4) (value is represented as hex value), null sometime
not_valid_before	datetime	not_before	datetime
not_valid_after	datetime	not_after	datetime
issuer_dn	string	ca (which is found using the DB name)	N/A
subject_dn	string	distinguished_name	str
pem	bytes	RawCertificate (but not in pem format)	N/A