Replace / improve "ideal"-image

[levino]

The current image implementation plugin-ideal-image looks not very ideal to me. The created html output is not using very powerful features like the srcset artribute for img tags. I think there might be potential in using nextjss Image component also for docusaurus and dropping the currently used dependency to react-ideal-image (or better the fork of the fork of the fork of it...).

Important features the new component should have:

• Use loading="lazy"
• Use srcset
• Optionally start with a srcset which has just one blurhash and replace that when the image is in the viewport with the "real" srcset.
• Set width and height correctly based on the input image.

[slorber]

I am aware this legacy plugin is not ideal but it's not my top priority to improve it atm, considering users can create their own plugins in userland.

If you want to work on a better image plugin for Docusaurus, you are welcome, and we might consider to make it the official one if it's proven successful