Create a migration doc from Playwright to k6

[ankur22]

What

We need a migration doc where we can guide users new to k6 on how to migrate their existing Playwright scripts to k6.

Why

At the moment users are left on their own to work through this problem, and if they have many scripts that need to be migrated they may not even attempt the process after completing/failing on migrating one script to k6. We want to help mitigate this risk.

How

We should detail things like:

1. Structural differences in the two (default export function vs the Playwright test package);
2. The differences in APIs (but also outline that we're adding more and point to the issues to show which APIs are coming soon);
3. How to configure tests vs Playwright configuration;
4. How to understand the output;
5. Point to the doc outlining the rational behind k6 + PW APIs (Rephrase "Rough Compatibility with Playwright" k6#4887);
6. Other areas that differ such as Chromium support only for now in k6.