Send device list updates to application services (MSC3202) - part 1 (#11881)

changelog.d/11881.feature

synapse/appservice/__init__.py

synapse/appservice/api.py

synapse/appservice/scheduler.py

synapse/config/appservice.py

synapse/config/experimental.py

synapse/handlers/appservice.py

synapse/handlers/sync.py

synapse/storage/databases/main/appservice.py

synapse/storage/databases/main/devices.py

.../68/06_msc3202_add_device_list_appservice_stream_type.sql

synapse/types.py

tests/appservice/test_scheduler.py

tests/handlers/test_appservice.py

tests/storage/test_appservice.py