Add new setting: prompt_column_separator

[pascal-pfeiffer]

closes #483

[sherenem]

Docs LGTM, thank you!

[psinger]

THX - overall looks good!

A little feedback:

• Shall we add a different default separator, like \n###\n or similar?
• I guess it is not possible to add a nesting that only triggers if multiple values are selected? Possible probably, but some work, not sure if worth.
• Otherwise I would suggest to add it to the tokenizer section though. It is a bit dominant on top.

[psinger]

Should this be an empty string by default?

[pascal-pfeiffer]

It was double space before, which is hard to see in the textbox and also a bit unusual. Decided to change it to double newlines now. Will push the changes in a bit. Wdyt?

[pascal-pfeiffer]

• Shall we add a different default separator, like \n###\n or similar?

After some thought, I decided to use \n\n, will push the changes in a bit.

• I guess it is not possible to add a nesting that only triggers if multiple values are selected? Possible probably, but some work, not sure if worth.

I also thought about it, but couldn't find an easy way. It would also force us to use a trigger for the columns dropdown.

• Otherwise I would suggest to add it to the tokenizer section though. It is a bit dominant on top.

From a logical standpoint, I believe it should be a dataset setting.