title: CNContactPickerViewController enable to disable multiple selection
body: <p>I want to enable or disable multiple contact selection based to condition.</p>
  <p>I have tried below solution</p>
  <pre><code>func onClickPickContact() {
          let contactPicker = CNContactPickerViewController()
          contactPicker.delegate = self
          contactPicker.displayedPropertyKeys =
              [CNContactGivenNameKey
                  , CNContactPhoneNumbersKey]
          self.present(contactPicker, animated: true, completion: nil)
      }
  
  func contactPicker(_ picker: CNContactPickerViewController, didSelect contact: CNContact) {
          self.txtFieldFirstname.text = contact.givenName
          self.txtFieldLastname.text = contact.familyName
      }
  </code></pre>
  <p>This allows me to select multiple contacts but I want both the cases (single selection or multiple selection based on condition).</p>
  <p>Once the above delegate method is added it is not allowing to select single contact only.</p>
  <p>Please Let me know if anyone knows the solution.
  Thanks in advance.</p>