Utilities.formatDate(new Date(), "GMT+1", "dd/MM/yyyy")
You can change the format by doing swapping the values.
function changeDate() {
var sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName(GA_CONFIG);
// You could use now Date(); on its own but it will not look nice.
var date = Utilities.formatDate(new Date(), "GMT+1", "dd/MM/yyyy")
var endDate = date
}