Feature: update node to version 20 as checkout v4 standard operates with v20

[commjoen]

What kind of changes does this PR include?

• Fixes or refactors
• A new challenge
• Additional documentation
• Something else : update to node version v20 with corrections in instructions on JDK as well

Description

Update to node version v20 with corrections in instructions on JDK as well.

Relations

NA

References

actions/checkout#1436
https://endoflife.date/nodejs

Checklist:

• All the contributions made are solely the work of me and my co-authors
• I tested the changes in this PR (if applicable)
• I added unit tests to ensure my change works (when change in Java or on front-end code)
• I added UI tests to ensure my UI changes work (when change in the overall UI, not needed if just adding a challenge)
• The PR passes pre-commit hooks and automated tests