Update Modules and JavaScript Compatibility Mode docs

[ppcano]

What?

• Update Using k6 / Modules
  • Restructure the ToC
  • Remove the unnecessary webpack instructions
  • Add Sharing JavaScript modules section
  • Add a minor Using TypeScript section
  • Add sections about Extension modules
  • Closes Document best practices to install extensions with Docker
• Update Using k6 / JavaScript Compatibility Mode
  • Closes Make the point that compatibility-mode=base is a lot less useful now
• Add a note to Extensions / Build a k6 binary using Docker

Checklist

Please fill in this template:

• 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 make docs command locally and verified that the changes look good.

[ppcano]

@mstoykov please, could you provide a technical review and share any suggestions?

[heitortsergent]

I reviewed the next files, I just left a few comments with some small edits to follow our style guide. It would be great to still get a technical review before we merge.

[ppcano]

Suggestions from @heitortsergent are now included and ported to previous versions. Additionally, all the changes were ported to v0.49.

It would be great to still get a technical review before we merge.

cc @mstoykov

[mstoykov]

LGTM in general

Left some comments around stuff that I think might be better

[ppcano]

@heitortsergent, I have addressed all the requests, and seems ready for the merge.