h2o 3.44.0.3 does not support JDK/Java 21

[ispringer]

Is your feature request related to a problem? Please describe.
H2O fails to initialize with error "Only Java versions 8-17 are supported, system version is 21.0.2" if JDK 21 is being used

Describe the solution you'd like
Support JDK 21

Describe alternatives you've considered
This is preventing me from upgrading my project to Java 21. All other libs we use support Java 21.

[mn-mikke]

It's on the roadmap. This issue duplicates #15772