Support unrolling lists of objects in the output

[lowell80]

List of objects should result in unrolling the of the list into multiple output events. Essentially, this is replacing the need for a secondary mvexpand command.

So if the jmespath expression results in

[
   { "A" : 4, "B": 9 },
   { "A" : 1, "B": 2 }
]

Then the input result/event should be cloned and returned twice. The first time with A=4, B=9 and the second event should have A=1,B=2.

Without this, a list JSON strings could be returned, which then requires mvexpand followed by another spath.