Docusaurus: Detect internal broken links during build

[omry]

🚀 Feature

A website should fail to build if it has internal broken links.

Have you read the Contributing Guidelines on issues?

Not relevant for feature requests, is it?

Motivation

While building the website, it's all to easy to change the page filename and forget or miss incoming internal links.

Pitch

It will help create higher quality websites and reduce the churn of "easy" incoming pull requests fixing minor issues in the docs.

[slorber]

agree, this is definitively something we need

[slorber]

check #3059

[omry]

awesome, that was quick!