This updates the K6 module documentation to show a JUnit-style example test, not just the container setup and script snippet.

The docs now include the existing K6ContainerTests flow so users can see the expected test shape end-to-end:

• configure the container
• start the container
• wait for the test run output
• assert on the logs

This keeps the existing codeinclude documentation style and reuses the tested source snippet instead of duplicating code in the docs.

Fixes #8780