[Snippets] Responsive images sizes

[stafyniaksacha]

At this time, only fixed width/height parameters are available.

We need to be able to define sizes instead if we want to serve images at the optimal size depending on screen.

This can be done easily if we keep the same aspect ratio. If we want other ratio, we can generate them using position/resize sharp filters.

A UI will be required to preview the result of those filters (more generally, we may need a UI to preview all sharp/ipx filters in real time)

We can then apply those ratios with pixel density and formats filters in snippet generation.

• Nuxt Image: Performance and Status nuxt/image#563
• https://v1.image.nuxtjs.org/configuration#screens
• https://developer.mozilla.org/en-US/docs/Learn/HTML/Multimedia_and_embedding/Responsive_images