chore: fix prettier config and run prettier on all files

[heitortsergent]

What?

• Update prettier configuration file to keep spacing in text between numbered list items

Fix the prettier configuration file to use the markdown parser instead of babel, and run prettier on the docs/sources folder. Hopefully this helps with the next PR reviews, as we've been getting small updates that end up with a lot of line changes because of prettier.

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.
• 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.

[jdbaldry]

Of course it's hard to vet all the changes but a scan through the PR before the patch was applied to previous versions looked fine to me. We can easily fix forward for some of the odd cases that prettier has resulted in different HTML output.

Would you like me to check any pages in particular? Perhaps the top 10 k6 pages in https://bi.grafana-ops.net/d/e7be048f-625e-486b-a4d3-37a393fe834f/docs-page-views?orgId=1&var-repository=All&var-path=%5E%2Fdocs%2Fk6?

[heitortsergent]

@jdbaldry I did a quick scan of the main sections and I think everything looks good as well. If people spot anything weird with the formatting, I think we can just fix it going forward. :)