Vel factory function

def create(policy_backbone: ModelFactory, value_backbone: ModelFactory,
           input_block: typing.Optional[ModelFactory]=None):
    """ Vel factory function """
    if input_block is None:
        input_block = IdentityFactory()

    return DeterministicPolicyModelFactory(
        input_block=input_block, policy_backbone=policy_backbone, value_backbone=value_backbone
    )