[Composition] Option to load external storybook minimized

[tim-mukhin]

I've already asked about this feature, but it seems, right now there is no option for that.
I want to add several external storybooks and it's not very convenient to scroll through llooooong list of every stories grom every storybooks.

refs: {
   name: {
      title,
      url,
      minimized: true  // add this option to refs. By default it's false
   }
}

[tim-mukhin]

Created PR with this feature #14345