Merge branch 'release-v0.18.4' of github.com:matrix-org/synapse

CHANGES.rst

docs/metrics-howto.rst

synapse/__init__.py

synapse/app/appservice.py

synapse/app/client_reader.py

synapse/app/federation_reader.py

synapse/app/media_repository.py

synapse/app/pusher.py

synapse/app/synchrotron.py

synapse/config/_base.py

synapse/config/password_auth_providers.py

synapse/config/repository.py

synapse/handlers/auth.py

synapse/handlers/message.py

synapse/http/server.py

synapse/metrics/__init__.py

synapse/metrics/process_collector.py

synapse/rest/client/transactions.py

synapse/rest/client/v1/base.py

synapse/rest/client/v1/room.py