Update README.md

[emmaaroche]

Description

The README needs to be updated to align with the Testsuite Setup Guide and to include documentation for the UI tests.

To Do

• Sync README content with the Testsuite Setup Guide
• Add a section for Playwright-based UI tests:
  • how to run them
  • required configuration
• Verify all current README content is still valid, and update anything that is outdated

Reference

Kuadrant Testsuite Setup Guide:
https://docs.google.com/document/d/1Y6b21AQtDuoJniU98LnXBHdinNobBKpkmCcY9Oy3rgM/edit?usp=sharing