BE: Migrate to Java 25

[yeikel]

• Breaking change? (if so, please describe the impact and migration path for existing application instances)

Updated the build and CI workflows to migrate from Java 21 to Java 25

What changes did you make? (Give an overview)

Closes #1349

Is there anything you'd like reviewers to focus on?

How Has This Been Tested? (put an "x" (case-sensitive!) next to an item)

• Integration checks
• Covered by existing automation

Checklist (put an "x" (case-sensitive!) next to all the items, otherwise the build will fail)

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (e.g. ENVIRONMENT VARIABLES)
• My changes generate no new warnings (e.g. Sonar is happy)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged

Docs pull request: kafbat/ui-docs#71

A picture of a cute animal (not mandatory but encouraged)

[yeikel]

@germanosin @Haarolean This pull request is ready for review

The build failure below occurs because these workflows run under pull_request_target, which means the workflow definitions from main are being used instead of my updated version that uses Java 25

However, I merged these workflow changes into the main branch of my fork, and you can see the successful build there: yeikel#269

[Incubating] Problems report is available at: file:///home/runner/work/kafka-ui/kafka-ui/build/reports/problems/problems-report.html
FAILURE: Build failed with an exception.

• What went wrong:
  Execution failed for task ':contract:compileJava'.

Java compilation initialization error
error: invalid source release: 25

[yeikel]

@Haarolean Thanks for the review. Do you have any feedback or what else is pending to move this forward?