Additional constants for EDU types. (#12884)

changelog.d/12884.misc

synapse/api/constants.py

synapse/api/filtering.py

synapse/federation/federation_server.py

synapse/federation/sender/per_destination_queue.py

synapse/federation/sender/transaction_manager.py

synapse/federation/transport/server/federation.py

synapse/handlers/appservice.py

synapse/handlers/device.py

synapse/handlers/devicemessage.py

synapse/handlers/e2e_keys.py

synapse/handlers/events.py

synapse/handlers/initial_sync.py

synapse/handlers/presence.py

synapse/handlers/receipts.py

synapse/handlers/typing.py

synapse/notifier.py

synapse/rest/client/sync.py

synapse/storage/databases/main/devices.py

synapse/storage/databases/main/receipts.py