Add endpoints for backfilling history (MSC2716) (#9247)

changelog.d/9247.feature

scripts-dev/complement.sh

synapse/api/auth.py

synapse/api/constants.py

synapse/config/experimental.py

synapse/events/__init__.py

synapse/events/builder.py

synapse/handlers/message.py

synapse/handlers/room_member.py

synapse/rest/client/v1/room.py

synapse/storage/databases/main/event_federation.py

tests/handlers/test_presence.py

tests/replication/test_federation_sender_shard.py

tests/storage/test_redaction.py