Merge remote-tracking branch 'origin/release-v1.47'

.ci/scripts/test_export_data_command.sh

.ci/scripts/test_synapse_port_db.sh

.github/PULL_REQUEST_TEMPLATE.md

CHANGES.md

contrib/purge_api/purge_history.sh

debian/build_virtualenv

debian/changelog

debian/control

debian/matrix-synapse-py3.config

debian/matrix-synapse-py3.postinst

debian/matrix-synapse.service

debian/test/.gitignore

debian/test/provision.sh

debian/test/stretch/Vagrantfile

debian/test/xenial/Vagrantfile

demo/clean.sh

demo/start.sh

demo/stop.sh

docker/README.md

docker/build_debian.sh