Initialize advanced attributes (`id`, `rel`) on link dialog open for new links in CKEditor 5

Adding Fix, Patches as welcome.

Between Line 96 - 102

96 - linkFormView[modelName] = extraFieldView;
linkFormView[modelName].fieldView
.bind('value')
.to(linkCommand, modelName);

 // Set the initial value explicitly in the command model if undefined
      if (typeof linkCommand[modelName] === 'undefined') {
        linkCommand.set(modelName, '');
      }  

102- // Note: Copy & pasted from LinkUI.
// https://github.com/ckeditor/ckeditor5/blob/f0a093339631b774b2d3422e2a579...
linkFormView[modelName].fieldView.element.value =
linkCommand[modelName] || '';
}

Hi!
Can you try with the latest 2.3.x dev version please?
I pushed some cleanup that, I think, should fix this issue.