fix(csv-stringify): allow mixed string and object columns typedef

[tusbar]

Since the code allows to specify the columns option as a mixed array of either string or ColumnOption, this updates the types accordingly.

See:

node-csv/packages/csv-stringify/lib/api/normalize_columns.js

Lines 19 to 45 in cc1235a

	for (const column of columns) {
	if (typeof column === "string") {
	newcolumns.push({
	key: column,
	header: column,
	});
	} else if (
	typeof column === "object" &&
	column !== null &&
	!Array.isArray(column)
	) {
	if (!column.key) {
	return [
	Error('Invalid column definition: property "key" is required'),
	];
	}
	if (column.header === undefined) {
	column.header = column.key;
	}
	newcolumns.push(column);
	} else {
	return [
	Error("Invalid column definition: expect a string or an object"),
	];
	}
	}
	columns = newcolumns;