[RateLimiter] Adding docs for rate limit sliding window

[Nyholm]

Does this makes sense? Do we understand how it works?

This will fix #14417

[wouterj]

Yes, I think it is. The idea of this document is to have something basic ready and then incrementally improve it.

E.g. I would love to have diagrams for each limiter showing the consequences (like the column images in https://medium.com/figma-design/an-alternative-approach-to-rate-limiting-f8a06cf7c94c [free medium article]). I think that should make things a lot clearer, but let's do it in a future PR

[javiereguiluz]

Tobias, thanks for contributing this nice feature and for updating the docs too. Cheers!

[Nyholm]

Thank you for the review and merge.