First attempt to migrate to java 21

[robfrank]

What does this PR do?

Migrate the code to java 21

Motivation

We need to stay more on the edge, IMHO

Checklist

• [x] I have run the build using mvn clean package command
• [x] My unit tests cover both failure and success scenarios

[lvca]

I hope (for you) the IDE converted all this code into Java21+! :-)

[robfrank]

not the IDE, openrewrite did: https://docs.openrewrite.org/recipes/java/migrate/javaversion21