Support number of histogram bins in approx_percentile_cont

[Ted-Jiang]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
like apache-hive

@Description(name = "percentile_approx",
    value = "_FUNC_(expr, pc, [nb]) - For very large data, computes an approximate percentile " +
            "value from a histogram, using the optional argument [nb] as the number of histogram" +
            " bins to use. A higher value of nb results in a more accurate approximation, at " +
            "the cost of higher memory usage.",
    extended = "'expr' can be any numeric column, including doubles and floats, and 'pc' is " +
               "either a single double/float with a requested percentile, or an array of double/" +
               "float with multiple percentiles. If 'nb' is not specified, the default " +
               "approximation is done with 10,000 histogram bins, which means that if there are " +
               "10,000 or fewer unique values in 'expr', you can expect an exact result. The " +
               "percentile() function always computes an exact percentile and can run out of " +
               "memory if there are too many unique values in a column, which necessitates " +
               "this function.\n" +
               "Example (three percentiles requested using a finer histogram approximation):\n" +
               "> SELECT percentile_approx(val, array(0.5, 0.95, 0.98), 100000) FROM somedata;\n" +
               "[0.05,1.64,2.26]\n")

Need add args max_size of tdigest(aka histogram bins) in approx_percentile_cont,
when calculate large amount data we need more sample points to keep accuracy.

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