Document 'experimental_enhanced' compatibility mode

[joanlopez]

What?

It documents the new experimental_enhanced compatibility mode.

Checklist

• I have used a meaningful title for the PR.
• I have described the changes I've made in the "What?" section above.
• I have performed a self-review of my changes.
• I have run the npm start command locally and verified that the changes look good.

• I have made my changes in the docs/sources/next folder of the documentation.
• I have reflected my changes in the docs/sources/v{most_recent_release} folder of the documentation.
• I have reflected my changes in the relevant folders of the two previous k6 versions of the documentation (if still applicable to previous versions).

• I have made my changes in the docs/sources/next folder of the documentation.

Related PR(s)/Issue(s)

• Related with TypeScript and ES6+ support using esbuild. k6#3738
• Related with Add link to new TS compatibility mode k6-template-typescript#50

We might also want to update:

• https://github.com/grafana/k6-jslib-aws/blob/main/CONTRIBUTING.md
• https://github.com/grafana/k6-rollup-example
• https://grafana.com/blog/2024/05/02/setting-up-your-grafana-k6-performance-testing-suite-javascript-tools-shared-libraries-and-more/

[joanlopez]

Thanks so much @heitortsergent! 💟