Playwright improvements

[hassy]

Description

• Update a Playwright TypeScript example to show how to use a before hook
• Disable worker threads for Playwright tests:
  • Fixes/avoids current issue of load tests written in TypeScript not respecting phases config. Because each worker re-imports the script, the original phase configuration is preserved, which leads to the load being multiplied rather than distrubuted.
  • There's no performance benefit to multiple threads in this case anyway because the actual work will happen in an external Chrome process

Pre-merge checklist

This is for use by the Artillery team. Please leave this in if you're contributing to Artillery.

• Does this require an update to the docs? No
• Does this require a changelog entry? Yes