`VaCarousel` navigation as image previews

[aluarius]

Add thumbnails as dots feature.

Ref: https://quasar.dev/vue-components/carousel#example--thumbnails

[asvae]

So, for this to work properly with a big number of images - we need to use smaller images for previews.

But for now - we don't have lazy loading. All images are loaded anyway!

So let's just add a warning in docs for this example. Saying something like "Carousel does not support lazy loading, so we suggest limiting a number and size of images."