Allow batch mode to be plain text newline delimited not just Array JSON

[bpb]

Currently batch mode forces JSON format.
There are instances where the data payload should be raw text but new line delimited where we do not need to send the data as json.
Would be useful to have this option.

[davidradl]

@bpb I think it is unusual to have a bespoke non-json , non-XML API that returns CSV records. I suggest you write your own custom format to convert your payload into JSON. If others in the community find this useful you could provide this as a sample. It is not obvious to me that this would be appropriate to put in to the code base as a new top level format, as it is not standard. WDYT?