Adds the following useful methods to CertUtil:

1. encodeCert - produce the PEM-encoding given an X509Certificate object
2. subjectDN - produce a string version of the subject of the given X509Certificate object
3. generateCert - Produce a self-signed X509Certificate object given a key pair and validity period as a Duration and an overloaded method with notBefore and notAfter.

MR fixes to include DER encoding type, removing hardcoded Signature algorithm during X509 certificate generation and other minor fixes.

Fix to include UTF_8 charset.

Push the encoding implementation into specific class types.

Rename canonX500PrincipalFormat.CANONICAL to X500PrincipalFormat.READABLE