Add fields-like option to peek to filter JSON and to reduce number associated commands

[sureshjoshi]

Having a GH CLI-like "fields" option would be nice, to a to allow consumers to limit the peek JSON they are returned (similar to a tool like jq).

However, in my opinion, this mostly makes sense if the "fields" will help performance by not performing the associated peek goals/rules - as otherwise we're scope creeping a poor man's jq into our CLI which feels excessive.