function addApprovalColumn(sheet, beginningRow, numRows) {
  sheet.insertColumnAfter(COLUMN_NUMBER.CALC_PAY);
  sheet.getRange(1, COLUMN_NUMBER.APPROVAL).setValue('APPROVAL');

  // Make sure approval column is all drop-down menus.
  let approvalColumnRange = sheet.getRange(beginningRow, COLUMN_NUMBER.APPROVAL,
      numRows, 1);
  let dropdownValues = ['APPROVED', 'NOT APPROVED', 'IN PROGRESS'];
  let rule = SpreadsheetApp.newDataValidation().requireValueInList(dropdownValues)
      .build();
  approvalColumnRange.setDataValidation(rule);
  approvalColumnRange.setValue('IN PROGRESS');
}
Adds an APPROVAL column allowing managers to approve/
disapprove of each employee's timesheet.

@param {Object} sheet Spreadsheet object of current sheet.
@param {Integer} beginningRow Index of beginning row.
@param {Integer} numRows Number of rows currently in use.