Congruence values count

[joein]

Methods value_counts, isempty, isnull didn't work properly in local mode due to an approach when we flatten all input values into one array

For instance if we have the following payload: {"nested": [{"numeric": 1, "numeric": 2, "numeric": 3}]} and want to filter by value count of numeric, then local mode piles up everything into one array and counts them together (values_count=3), but it should count them separately (values_count=1)

Another problem with payload like
{"nested": [{"empty": [None]}, {"empty": [None]}, {"empty": [None]}
or
{"nones": [None, None]}

Local mode considers such fields equal to None, however [None, None] != None.

This PR adjusts interface of payload_value_extractor and allows to disable flattening during an extraction of values.

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