FINERACT-2094 Upgrade to JDK 21 LTS

[IOhacker]

Description

Describe the changes made and why they were made.

Upgrade JDK 17 LTS to JDK 21 LTS Upgrade Gradle file (Jib) for building in a JDK 21 LTS docker image. Upgrade Github actions for using JDK 21 LTS

Checklist

Please make sure these boxes are checked before submitting your pull request - thanks!

• [X] Write the commit message as per https://github.com/apache/fineract/#pull-requests

• [X] Acknowledge that we will not review PRs that are not passing the build ("green") - it is your responsibility to get a proposed PR to pass the build, not primarily the project's maintainers.

• [ ] Create/update unit or integration tests for verifying the changes made.

• [ ] Follow coding conventions at https://cwiki.apache.org/confluence/display/FINERACT/Coding+Conventions.

• [ ] Add required Swagger annotation and update API documentation at fineract-provider/src/main/resources/static/legacy-docs/apiLive.htm with details of any API changes

• [ ] Submission is not a "code dump". (Large changes can be made "in repository" via a branch. Ask on the developer mailing list for guidance, if required.)

FYI our guidelines for code reviews are at https://cwiki.apache.org/confluence/display/FINERACT/Code+Review+Guide.

[IOhacker]

@jdailey

[vidakovic]

Just one caveat: we can run ON JDK 21, but we can not compile TO JDK 21 language version... Eclipse Link is only supporting Java 17. FYI

[github-actions[bot]]

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