Convert calls of async database methods to async (#8166)

changelog.d/8166.misc

synapse/federation/persistence.py

synapse/federation/units.py

synapse/storage/databases/main/appservice.py

synapse/storage/databases/main/devices.py

synapse/storage/databases/main/group_server.py

synapse/storage/databases/main/keys.py

synapse/storage/databases/main/media_repository.py

synapse/storage/databases/main/openid.py

synapse/storage/databases/main/profile.py

synapse/storage/databases/main/registration.py

synapse/storage/databases/main/room.py

synapse/storage/databases/main/stats.py

synapse/storage/databases/main/transactions.py