Introduce linting for documentation to ensure that it is all valid

[Yantrio]

As we are introducing docusaurus, we need to ensure that all links in the mdx files are valid and resolve correctly.

This may get chunked up into multiple sections of work so we can distribute the effort accordingly.

The initial step of this is to add linting to the main repo

[codiini]

@Yantrio I think this issue can be closed since the corresponding PR was merged :)

[janosdebugs]

Thanks @codiini !