Allow images to fall back to unoptimized state when URL does not match remotePatterns

[art-alexeyenko]

Goals

1. Have image be displayed at all times
2. Avoid rendering errors when image source has not been added to remotePatterns
3. Better editor experience when nextjs site is used for editing (and when images from 3rd party sources are used)

Non-Goals

No response

Background

Current next image approach is very uncompromising: either an optimized image is rendered or the image is missing if it doesn't match remotePatterns. In case of editing site layout adding an image can sometime lead to empty display.
One alternative is to specify a very lax remote pattern which defeats the purpose a bit.
Another is to basically copy nextjs's pattern matching logic and dynamically apply "unoptimized" when image src does not match patterns. It would be best for nextjs to have the option to do this dynamic unoptimized fallback out of the box.

Proposal

Add an unoptimizedFallback boolean attribute to next image component. When it's enabled and image's src does not match remotePatterns, the image's unoptimized attribute will be set to true and image will render as is.

PR with possible solution: art-alexeyenko#1 , will post to nextjs repo if feature request is approved.