Filter out NULLS in aggregation function

[KKcorps]

The queries like COUNT(columnA) should only count rows which have non-null values.
e.g.
A column int0 has 17 rows out of which 6 have nulls
in pinot COUNT(column) will return 17
but it should ideally return 11.

[richardstartin]

This is supported by filter clauses which will be released in 0.10.0. Making it the default behaviour is another question.

[KKcorps]

Just saw it. #7916 has these changes. I think that should suffice for now.