Upgrade unleash to avoid requiring Java 11 for deployment

[holgerfriedrich]

Our release workflow depends on the unleash-maven-plugin which requires Java 11.
We have set certain steps in the CI to run on Java 11, whereas the compilation etc. is currently on Java 21.

When we switch to a newer Java release - and this is getting more and more important -, we run into issues:
#1540
#1475

A possible solution is to migrate to a different version of the unleash plugin, which is maintained and supports Java 21:
#1475 (comment)

Therefore, we need to touch the super-pom, as mentioned here:
openhab/static-code-analysis#494 (comment)

A non-invasive approach is desired, i.e. for a transition phase, both the old plugin and the new plugin should be usable for the releases. This could for example be done using profiles (depending on the Java version),

[holgerfriedrich]

@wborn @kaikreuzer WDYT? Does an approach as outlined in openhab/infrastructure#20 make sense?

Any recommendation how can we test this?

[lsiepel]

Gentle ping @openhab/distro-maintainers Would be nice as it also enables to update the checkstyle version.

[holgerfriedrich]

@lsiepel There is some progress.

I can comment on SAT plugin:
SAT plugin is now released using GHA. Kai has released 0.18.0 which still requires Java 11 (put already supports checking Java 25 classes with new PMD). Checkstyle upgrade is still blocked by Java 11. I am preparing openhab/static-code-analysis#535 to move to Java 21.

I cannot tell about other blockers in the release process still on Jenkins and unleash plugin.
Maybe SAT is completely independent and no further action is required.