Add rate-limiting on registration (#4735)

* Rate-limiting for registration

* Add unit test for registration rate limiting

* Add config parameters for rate limiting on auth endpoints

* Doc

* Fix doc of rate limiting function

Co-Authored-By: babolivier <contact@brendanabolivier.com>

* Incorporate review

* Fix config parsing

* Fix linting errors

* Set default config for auth rate limiting

* Fix tests

* Add changelog

* Advance reactor instead of mocked clock

* Move parameters to registration specific config and give them more sensible default values

* Remove unused config options

* Don't mock the rate limiter un MAU tests

* Rename _register_with_store into register_with_store

* Make CI happy

* Remove unused import

* Update sample config

* Fix ratelimiting test for py2

* Add non-guest test