Is your feature request related to a problem? Please describe.
The image block allows adding images via a URL. It would be helpful to allow this also for Cover image.
This is a screenshot from the newly released Gutenberg Playground.

There is not access to upload images but to demo the Cover block here it would be necessary, to have a way to add an image via URL.

Describe the solution you'd like
Similar to the image placeholder offering three buttons and if access to the media library or to upload is not available hide those buttons and only leave the "Insert from URL" button

Although I describe the need for the "Insert Image via URL" in the context of the Playground site, I can easily imagine that it expands the ease of use for the cover block in any implementation context.