[list] Split list command into list-datasets and list

[viklund]

As a user of sda-cli
I want to have clear commands for each action
so I'm less confused

Description

We should probably not do the noun verb thing here because that would go against how all the other subcommands work.

The list --datasets subcommand should be split out into it's own command called list-datasets. list should always and only list files in a dataset.

A/C

Demo

Run the commands, 3 minute demo.