How to dynamically add the the input text field in widget?

How about jQuery append method?
To make a counter, simply increment i variable every click.

$('body').on('click', '.add-more-button', function() {
  var i = 2;
  $('.widget-input').append('<label>Link' + i + '</label><input>');
  i++;
}

This is just an idea, I guess someone more experienced can develop it further.