Add option for JSON viewer to select a key to display against an array entry in the tree

[AdyRock]

When there is a large JSON array, it would be great to be able to select a key whose value can be displayed next to the index number. At the moment I see:
[0]:[Object]
[1]:[Object]
etc, but when the array has over 100 entries, it takes a long time to find the ones I might want to look at. If I could select a key, such as "label" and show the value:
[0]:[Object] ("Don't care")
[1]:[Object] ("Do Care")
etc, it would be great.

[AntunBartonicek]

Can be merged with NPP-JSONViewer/JSON-Viewer#76