[FEA] Assert that on connecting to cluster you have at least > 1 workers

[VibhuJawa]

Is your feature request related to a problem? Please describe.

We need to assert > 1 worker

We need to add a check after this : https://github.com/NVIDIA/NeMo-Curator/blob/9a424c7a498519aeb971a3453ae71447b952b500/nemo_curator/utils/distributed_utils.py#L156