minor #14436 [RateLimiter] Add diagrams to better explain the differences (wouterj)

This PR was submitted for the 5.x branch but it was merged into the 5.2 branch instead.

Discussion
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[RateLimiter] Add diagrams to better explain the differences

This is just a POC to add some diagrams to better explain the differences in the rate limiter strategies.

Commits
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1cdb6cb Added limiter diagrams

Author: javiereguiluz