Merge branch 'develop' into jaywink/admin-forward-extremities

.buildkite/scripts/create_postgres_db.py

changelog.d/9036.feature

changelog.d/9038.misc

changelog.d/9039.removal

changelog.d/9051.bugfix

changelog.d/9053.bugfix

changelog.d/9054.bugfix

changelog.d/9057.doc

demo/webserver.py

docs/openid.md

mypy.ini

stubs/frozendict.pyi

stubs/sortedcontainers/sorteddict.pyi

stubs/txredisapi.pyi

synapse/config/_util.py

synapse/notifier.py

synapse/rest/client/v1/login.py

synapse/storage/databases/main/client_ips.py

synapse/util/metrics.py

tests/config/test_util.py