[all] (#330) Support for Java version 21 LTS

[Tchoui]

Description

Upgraded Java Version to latest LTS - Java 21.
Closes #330

Checklist

• I have added necessary documentation, relevant usage information (if applicable)
• I have updated the PR title with affected component, related issue number and a short summary of the changes introduced
• I have tested against live environment, if applicable
• I have my changes rebased and squashed to the minimal number of relevant commits. Notice: don't squash all commits
• I have added a descriptive commit message with a short title, including a Fixed #XXX - or Closed #XXX - prefix to auto-close the issue

Testing

Tested by @VenelinBakalov on live environment with various current project.

Release Notes

Upgraded Java version to Java 21 LTS in github workflow files.
Upgraded Jacoco maven plugin to 0.8.12 for Java 21 support.
Added property java.version in the main pom.xml file, now the java version can be changes from a single place for the whole code. Note that java version still has to be updated manually in all workflow and documentation files.
Java version for the code is still Java 17 LTS

Related issues and PRs

Closes #330.

[VenelinBakalov]

Any additional tests and feedback is welcome. So far tested on Mac OS with JS, TS, XML, vRA NG and Polyglot project.

[Michaelpalacce]

@Tchoui LGTM :) I think we can close it, if anyone has any issues later on we can revert this.