Please make the MapBuilder values_field nullable a configurable value

[alanhe]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
With MapBuilder, it's not possible to build the sample schema described in the spec: https://github.com/apache/parquet-format/blob/master/LogicalTypes.md#backward-compatibility-rules-1

optional group my_map (MAP) {
  repeated group map {
    required binary str (UTF8);
    required int32 num;
  }
}

because in Line 141, nullable is hard-coded to true.

arrow-rs/arrow/src/array/builder/map_builder.rs

Lines 138 to 142 in 3096591

	let values_field = Field::new(
	self.field_names.value.as_str(),
	values_arr.data_type().clone(),
	true,
	);

So, it will also be optional int32 num.

Describe the solution you'd like
Can we make it configurable?

[Weijun-H]

After reviewing the code, it appears that the bug has been resolved.

arrow-rs/parquet/src/arrow/schema/mod.rs

Lines 991 to 1014 in 96791ea

	// // Map<String, Integer> (nullable map, non-null values)
	// optional group my_map (MAP) {
	// repeated group map {
	// required binary str (UTF8);
	// required int32 num;
	// }
	// }
	{
	arrow_fields.push(Field::new(
	"my_map2",
	DataType::Map(
	Box::new(Field::new(
	"map",
	DataType::Struct(vec![
	Field::new("str", DataType::Utf8, false),
	Field::new("num", DataType::Int32, false),
	]),
	false, // (#1697)
	)),
	false,
	),
	true,
	));
	}