Implement vale linter

[andreslucena]

To be consistent with the documentation repositoty, we should implement the vale linter with the same rules.

See https://github.com/decidim/documentation/pull/147 for more details.

As @RCheesley said there:

Vale is a tool which lints - checks - text against certain pre-specified rules - much like similar tools for software development highlight and/or fix code style issues.

This helps to improve the quality of written text, pick up problems such as typos or grammar issues, and also can help to flag up words or phrases which might in some situations or cultures be inappropriate.

I have implemented two style plugins from Vale - Google and Alex.

Google's technical writers styleguide is a well-used developer technical style guide which covers a huge amount of grammar issues and best practices, and it also picks up some inappropriate word use.

Alex is more focused on the cultural sensitivity and appropriateness of words used.

This allows writers to check their text as they're writing (for example there are plugins for VSCode, PHPStorm etc) and it also allows us to check PRs which are made so that if we haven't fixed those files yet, they can be cleaned as we go and new contributions can be checked to ensure they adhere to the style guides.

(The first link is wrong, it should be https://vale.sh/)

We should implement it here (in decidim/decidim) after we finish the implementation in the documentation repository (decidim/documentation).

This is also related to the changes from #10553 and #8684 (both of these rules should be migrated to Vale)

[RCheesley]

Would you like me to implement it here as well, @andreslucena ?