add cert auth example in devguide-examples

In support of users of the devguide-examples and possible high-level conceptual documentation and other samples being created, add on master branch of devguide-examples an example of enabling certificate authentication through the CertificateAuthenticator.

Given a script that generates the CA, any intermediate certs, the cluster node certs and client certs, the sample should show how to use or import the given cert from a file into the appropriate SDK to use with a cluster node in the same chain of trust.

Use the PHP example as a pattern as seen in PCBC-540.