COOPR-520: Add mutual auth support

Please review
Better initialize the `TrustManager[]` inside the `if` clause above and use it here directly. E.g.

```java
KeyManager[] keyManagers = kmf.getKeyManagers();
TrustManager[] trustManagers = null;
if (sslConfig.getTrustKeyStore() != null) {
  ...
  TrustManagerFactory factory = TrustManagerFactory.getInstance(algorithm);
  factory.init(tks);
  trustManagers = tmf.getTrustManager();
}
serverContext.init(keyManagers, trustManagers, null);