[docs-infra] Add Vale integration for automatic style and grammar linting

[samuelsycamore]

Summary 💡

I've been talking about this with @oliviertassinari for quite awhile now, and it's time to move forward with it!

Vale is a command-line tool that brings code-like linting to prose.

With Vale, we can translate our Style guide into a set of rules that live within the Core and X repos.

Running Vale as a command line tool on a document gives you a list of suggested changes based on our house rules.

That's pretty cool on its own, but it's even cooler when you add the GitHub Action.
Whenever you create or edit an .md file, it will automatically run Vale and leave line-by-line suggestions:

It appears that most of the work is just formatting the style rules. I've started that process today, and I'll open a PR once I have something to show for it. From there, I'll test it out on some docs with the CLI, tweak as needed, then move on to set up the Action.

Motivation 🔦

This will be a huge help when writing new docs and blog posts, especially for the non-native English speakers on the team.

I believe it will also go a long way towards expediting the work that needs to be done to implement the Style guide across the entire docs site, and it will make it much easier for anyone to jump in and contribute to that work.

[vj-codes]

@samuelsycamore hey I've worked with GitHub action integrations before, can I work on this?

[oliviertassinari]

MUI X using Vale since mui/mui-x#5429.

[samuelsycamore]

If the X team has found it useful, then let's go for it! We should be able to copy their style guide rules over easily enough.