While working on https://github.com/matrix-org/synapse/issues/5665 I found myself digging into the `Ratelimiter` class and seeing that it was both:
* Rather undocumented, and
* causing a *lot* of config checks
This PR attempts to refactor and comment the `Ratelimiter` class, as well as encourage config file accesses to only be done at instantiation.
Best to be reviewed commit-by-commit.
* 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
