JVMCBC-1686 CertificateAuthenticator.toString() can include unprotected private key

Motivation
----------
Prior to this change, the toString() method of an authenticator
created by CertificateAuthenticator.fromKey() includes the private key.
This could potentially result in the private key appearing in
application logs -- but only if the user explicitly logs the authenticator.

Modifications
-------------
Change CertificateAuthenticator.toString() to return just
"CertificateAuthenticator".

Omit `keyManagerFactory` because it's a supplier whose
toString() is not interesting.

Omit `keyCertChain` because it's not particularly useful.

Change-Id: I733830eb8784f9c0195074903544ee8eb42ce334
Reviewed-on: https://review.couchbase.org/c/couchbase-jvm-clients/+/233953
Tested-by: Build Bot <[email protected]>
Reviewed-by: Michael Reiche <[email protected]>

Author: dnault

core-io/src/main/java/com/couchbase/client/core/env/CertificateAuthenticator.java

@@ -158,11 +158,8 @@ public boolean supportsNonTls() {
 
   @Override
   public String toString() {
-    return "CertificateAuthenticator{" +
-      "key=" + key +
-      ", keyCertChain=" + keyCertChain +
-      ", keyManagerFactory=" + keyManagerFactory +
-      '}';
+    // Intentionally omit sensitive info like private key.
+    return "CertificateAuthenticator";
   }
 
 }