[Feature] Implement batching for file based executors

[jan-janssen]

For the SingleNodeExecutor, SlurmJobExecutor and FluxJobExecutor it is implemented in #756 . Still the functionality is not yet available in the SlurmClusterExecutor and the FluxClusterExecutor.

[jan-janssen]

The challenge is that most queuing systems do not support this option, the only thing they can do is wait until all future objects are completed. But at that point there is no advantage of using the batched option, so it is also fine to not have this option implemented for the SlurmClusterExecutor and the FluxClusterExecutor.