Message type needs to be dataset when message contains dataset in posttroll-hook

[TAlonglong]

It look to me that the hook can produce both messages with file and dataset.

But the message type is hardcoded to file.

https://github.com/pytroll/pytroll-pps-runner/blob/main/nwcsafpps_runner/pps_posttroll_hook.py#L274

I think this needs to be fixed

[TAlonglong]

OK this is maybe to as as easy.

Why is it necessary to use dataset? If this message is to be send to move-it-server it will fail.

I there for suggest to not use dataset at all, but make individual messages for each file in the dataset and this avoid the dataset problem

The code to make the mesage is about here:
https://github.com/pytroll/pytroll-pps-runner/blob/main/nwcsafpps_runner/pps_posttroll_hook.py#L335-L351

I suggest we loop over the dataset and generate a message for each file.