function checkFolder() {
  const folders = DriveApp.getFoldersByName('Agenda Maker - App');
  // Finds the folder if it exists
  while (folders.hasNext()) {
    let folder = folders.next();
    if (
      folder.getDescription() ==
        'Apps Script App - Do not change this description' &&
      folder.getOwner().getEmail() == Session.getActiveUser().getEmail()
    ) {
      return folder.getId();
    }
  }
  // If the folder doesn't exist, creates one
  let folder = DriveApp.createFolder('Agenda Maker - App');
  folder.setDescription('Apps Script App - Do not change this description');
  return folder.getId();
}
Checks if the folder for Agenda docs exists, and creates it if it doesn't.

@return {*} Drive folder ID for the app.