Rename storage classes (#12913)

changelog.d/12913.misc

synapse/events/snapshot.py

synapse/federation/federation_server.py

synapse/handlers/admin.py

synapse/handlers/device.py

synapse/handlers/events.py

synapse/handlers/federation.py

synapse/handlers/federation_event.py

synapse/handlers/initial_sync.py

synapse/handlers/message.py

synapse/handlers/pagination.py

synapse/handlers/relations.py

synapse/handlers/room.py

synapse/handlers/room_batch.py

synapse/handlers/search.py

synapse/handlers/sync.py

synapse/notifier.py

synapse/push/httppusher.py

synapse/push/mailer.py

synapse/push/push_tools.py