gRPC protocol updates

[olegbespalov]

What?

This PR aims to fill the gaps mentioned by @dgzlopes and provide a complete overview of the gRPC support in k6.

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.

Select one of these and delete the others:

If updating the documentation for the most recent release of k6:

• 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 (e.g. when correcting a documentation error) folders of the previous k6 versions of the documentation.

If updating the documentation for the next release of k6:

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

Related PR(s)/Issue(s)

Closes #1378
Closes #1038

[olegbespalov]

I'm wondering if that section deserves a dedicated page in k6/net/grpc JavaScript's API 🤔

The main reason why I haven't put it there is that Marshaling/Unmarshaling is not an API. But probably, it is worth cross-linking from the Invoke/Stream.on pages to this section once it is merged (don't want to do this in a single PR since there is a #1472 PR which could cause a lot of conflicts)

WDYT?

[dgzlopes]

But probably, it is worth cross-linking from the Invoke/Stream.on pages to this section once it is merged (don't want to do this in a single PR since there is a #1472 PR which could cause a lot of conflicts)

Yeah, let's do this 👍

[codebien]

@olegbespalov Congrats and thanks for this. 🎉

It sounds like a very good starting point. @dgzlopes it would be good to know your feeling about it.

[dgzlopes]

This is great @olegbespalov! A much-needed improvement for this page. Thanks for working on it ❤️

LGTM

[dgzlopes]

But probably, it is worth cross-linking from the Invoke/Stream.on pages to this section once it is merged (don't want to do this in a single PR since there is a #1472 PR which could cause a lot of conflicts)

Yeah, let's do this 👍

[heitortsergent]

I left a few small comments, overall it looks great! 🚀 Glad we have more content and examples on this page. 🙇