Add draft for k6 new command docs

[heitortsergent]

What?

Adds a new page explaining the k6 new command and the new options available in k6 v0.57.

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/k6/next folder of the documentation.

Related PR(s)/Issue(s)

Closes #1857.

[heitortsergent]

@dgzlopes added you as a reviewer as well since you worked on this feature. 🤓

One thing I don't love about this is the section where it's in... I think it makes sense to live under "Test authoring", but I don't like how that's buried three levels deep in the docs.

One option, and something that @oleiade and I have been talking about, is maybe moving the "Test authoring" section all the way to the first level of the folder structure, next to "Set up" and "Using k6". Similar to how we have an "Author and run test" section in the GCk6 docs.

What do you think? 🤔

[dgzlopes]

@heitortsergent I think that's a good idea 👍

[dgzlopes]

LGTM

[olegbespalov]

Looks good to me, but please be aware that #1854 has been merged, so it's worth maybe to also reflecting along with next changes under v0.57.x

[heitortsergent]

Thanks for the reviews! I applied the changes to v0.57.x. I'll go ahead and merge this so we have the k6 new docs out, and open a separate PR to reorganize the sections.