Implement MSC3231: Token authenticated registration (#10142)

changelog.d/10142.feature

docs/SUMMARY.md

docs/sample_config.yaml

docs/usage/administration/admin_api/registration_tokens.md

docs/workers.md

synapse/api/constants.py

synapse/app/generic_worker.py

synapse/config/ratelimiting.py

synapse/config/registration.py

synapse/handlers/ui_auth/__init__.py

synapse/handlers/ui_auth/checkers.py

synapse/res/templates/registration_token.html

synapse/rest/admin/__init__.py

synapse/rest/admin/registration_tokens.py

synapse/rest/client/auth.py

synapse/rest/client/register.py

synapse/storage/databases/main/registration.py

synapse/storage/databases/main/ui_auth.py

...age/schema/main/delta/63/01create_registration_tokens.sql

tests/rest/admin/test_registration_tokens.py