Add Vale docs linting support

[theletterf]

This PR adds support for Vale docs linting to the repository. Linting only triggers when Markdown files inside the docs folder are edited. Vale linting never blocks pull requests. For more information, refer to Vale linter.

Contributes to https://github.com/elastic/docs-content-internal/issues/670

[pquentin]

Thanks! LGTM. I used Vale recently, and some suggestions are pretty good. I applied some of them in #3324.

But there's also a lot of noise. In the DSL client, we execute queries; this is even in the API, but Vale doesn't like it, for example.

[theletterf]

Interesting. Could you provide some examples? In theory, Vale only lints Markdown changed lines and ignores code blocks.

[pquentin]

Right, I'm talking about what Vale adds to the "Problems" tab in my editor. For example, we use "via" a lot and it doesn't like it.

There are many words like this. Consider this sentence:

In this example, you can see:

Vale suggests replacing "see" with "refer to" but that never works. Another example:

In addition to these, query_vector or query_vector_builder must be given as well.

Vale suggests replacing "In addition" with "Also", which doesn't work. Regarding execute, we have a lot of sentences like this:

You can execute your search by calling the .execute() method that will return a Response object.

It would be nice to silent some rules or allow some words on a per-project basis to avoid all the squiggly lines.

[theletterf]

Point taken! Could you raise some issues in the vale-rules repo?