Collect terms consent from the user during SSO registration (#9276)

changelog.d/9276.feature

docs/sample_config.yaml

docs/workers.md

synapse/config/sso.py

synapse/handlers/register.py

synapse/handlers/sso.py

synapse/res/templates/sso_new_user_consent.html

synapse/rest/synapse/client/__init__.py

synapse/rest/synapse/client/new_user_consent.py