Option to output all unique elements of a given metadata field

[matthuska]

In GitLab by @Alice_Wittig on Mar 13, 2022, 12:47

One thing I stumbled upon is that it would be very useful to be able to output the unique elements of the metadata collections, because you don't necessarily know them by heart.

I could imagine something like that:

sonar.py info --db mydb --collections

which would output: "collection_x", "collection_y", "collection_z"