Use static locations for Riot icons

Co-Authored-By: turt2live <travpc@gmail.com>

Prefill client IPs cache on workers

Add docstrings from matrix-org-hotfixes

Port #4422 debug logging from hotfixes

Send message after room has been shutdown

Currently the explanation message is sent to the abuse room before any
users are forced joined, which means it tends to get lost in the backlog
of joins.

So instead we send the message *after* we've forced joined everyone.

Support batch updates in the worker sender 

Improve ratelimit on registration

This reverts commit d7dbad35.

 Add 'server_version' endpoint to admin API

* 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

Remove reference to that no longer exists in README

Remove unnecessary dollar signs

Stop backpaginating when events not visible

Clean ups in replication notifier

 Allow /keys/{changes,query} API to run on worker

Add some debug about processing read receipts.

Clean up read-receipt handling.

Both (!) things that register as replication listeners do the right thing wrt
logcontexts, so this is redundant.