[Feature Request] Add a placeholder image to the image block

[samxmunoz]

Issue

If you don't have an image in mind while building with blocks, it can throw off the layout of a project to see a spaced "placeholder" on the editing view but nothing in the live version of the page.

Proposed Solution

Add a placeholder image to the image block (perhaps a landscape default placeholder with the WordPress logo, or allow a random placeholder pulled in from an API from a royalty free photo suite like Unsplash or even better, utilize Openverse).

If a WordPress logo default placeholder image, maybe something like these (created with ❤ by me using the Graphics & Logos open source imagery + Canva)

See it in action...

[colorful-tones]

This may be a duplicate of #41142

[annezazu]

I'm going to close this out as a confirmed duplicated. If there's something that feels distinctive about this issue though, just let me know and I'll reopen!