How can I add a Link field to my theme's settings? The link module is activated and being used on content types already, I can't work out how to use it in the theme's settings.

I've already got the code setup to add a URL but I want the editing experience to provide both the URL with auto-complete and link text.

$form['settings']['pop_up']['popup_cta'] = array(
  '#type'          => 'url',
  '#options'       => ['external' => TRUE],
  '#title'         => t('CTA'),
  '#description'   => t("The CTA for the pop-up."),
);

This is the link field I want: