Add autorun support for examples in gradle

[riccardobl]

No description provided.

[riccardobl]

@gemini-code-assist review

[github-actions]

🖼️ Screenshot tests have failed.

The purpose of these tests is to ensure that changes introduced in this PR don't break visual features. They are visual unit tests.

📄 Where to find the report:

• Direct Download: screenshot-test-report
• Alternatively, go to the failed run summary > Artifacts > screenshot-test-report
• Download the zip and open jme3-screenshot-tests/build/reports/ScreenshotDiffReport.html

⚠️ If you didn't expect to change anything visual:
Fix your changes so the screenshot tests pass.

✅ If you did mean to change things:
Review the replacement images in jme3-screenshot-tests/build/changed-images to make sure they really are improvements and then replace and commit the replacement images at jme3-screenshot-tests/src/test/resources.

✨ If you are creating entirely new tests:
Find the new images in jme3-screenshot-tests/build/changed-images and commit the new images at jme3-screenshot-tests/src/test/resources.

Note; it is very important that the committed reference images are created on the build pipeline, locally created images are not reliable. Similarly tests will fail locally but you can look at the report to check they are "visually similar".

See https://github.com/jMonkeyEngine/jmonkeyengine/blob/master/jme3-screenshot-tests/README.md for more information

Contact @richardTingle (aka richtea) for guidance if required

[gemini-code-assist]

Code Review

This pull request introduces a new runExamples Gradle task in the jme3-examples module, enabling users to run engine examples directly from the command line with an optional -Pexample property. Corresponding documentation has been added to the README.md. Feedback suggests improving the documentation's grammar and formatting for better readability. Additionally, it is recommended to refactor the runExamples task to be more idiomatic by moving the mainClass assignment to the configuration phase and using project.findProperty for safer access to the assertions property.