Use secureClientPort instead of clientPort

[maltesander]

Currently for TLS and authentication we use the clientPort instead of secureClientPort due to a bug in ZooKeeper (https://issues.apache.org/jira/browse/ZOOKEEPER-4276).

Once this is fixed and we should switch from clientPort to secureClientPort and remove the portUnification property (allows plaintext and secured communication via the same port).

The necessary steps are documented in the code (see rust/crd/src/lib.rs)

Since this does not work in versions 3.8.0 or lower, it will be a little more work to differentiate between zookeeper versions with and without that bug.

Relates to PR #479.

[sbernauer]

Good news, ZOOKEEPER-4276 was fixed and will be released in 3.10.0 🥳