switch to Java 21 for build/Docker

[vladak]

The bytecode target is still Java 11 to support older deployments.

I had to solve multiple issues:

• bump Mockito so that it uses newer Byte buddy library which supports Java 21
• address non-serializable members by either switching them to transient or using Serializable type
• avoid this leaks from constructors or suppress the warning
• udpate Chronicle Map so that it does not attempt to get method not present in Java 21

Tested the newly built Docker image with pre-existing data root. Also tested with JRE 11 on Solaris x86 with pre-existing data-root and semi-complex setup (authorization, suggester, annotation cache).