Added support for Java 21 and removed support for Java 11

[hbelmiro]

Fixes: #639

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Once the original pull request is successfully merged, the automated action will create one backporting pull request per each label (with the previous format) that has been added.

If something goes wrong, the author will be notified and at this point a manual backporting is needed.

NOTE: this automated backporting is triggered whenever a pull request on main branch is labeled or closed, but both conditions must be satisfied to get the new PR created.

[github-actions]

🎊 PR Preview 87e8a0b has been successfully built and deployed. See the documentation preview: https://quarkus-openapi-generator-preview-pr-640.surge.sh

[mcruzdev]

LGTM!

[ricardozanini]

Thank you!