Add TLS support

[adwk67]

tokio-zookeeper does not currently support TLS: this needs to be added before we can support Zookeeper 3.10 (or patch ZOOKEEPER-4276). Some of the unit tests fail and the code compiles with a warning. Recent additions (for release 25.11) are in main and need to part of a new release 0.5.0.

[lfrancke]

I understood that this is one option. Another option would be to switch to a different library, correct?
I'd like to have that clarified during a refinement.