--- features: - A new optional interface `TempestPlugin.get_service_clients` is available to plugins. It allows them to declare any service client they implement. For now this is used by tempest only, for auto-registration of service clients in the new class `ServiceClients`. - A new singleton class `clients.ClientsRegistry` is available. It holds the service clients registration data from all plugins. It is used by `ServiceClients` for auto-registration of the service clients implemented in plugins.