Stretch: [ngrok ConnectionOption] WithCA

[jtszalay]

Various connection options have yet to be surfaced. This is one of them.

// WithCA configures the CAs used to validate the TLS certificate returned by
// the ngrok service while establishing the session. Use this option only if
// you are connecting through a man-in-the-middle or deep packet inspection
// proxy.
//
// See the [root_cas parameter in the ngrok docs] for additional details.
//
// [root_cas parameter in the ngrok docs]: https://ngrok.com/docs/ngrok-agent/config#root_cas
func WithCA(pool *x509.CertPool) ConnectOption