Prepare 3.10.0

[Andor Molnár]

Hi team,

Let’s prepare for the 3.10.0 cut.

https://issues.apache.org/jira/projects/ZOOKEEPER/versions/12353481

191 issues done, 4 issues to do.

What’s missing?
What would you like to see finished before the initial release?

Regards,
Andor