[PP-1] Handle media image fields on page data form

Feel free to ping me when you dig into this; @bnjmnm is the real expert in that area, but happy to assist when @bnjmnm has more important things to tackle!

No longer relevant as this was addressed by other work. There is confirmation of this in the test 'Can open the media library widget in an xb_page props form' in media-library.cy.js (this test does more than just open, it adds / removes etc.)

Maybe there's something more specific that's wrong but this doesn't seem to be working for me? Attached video to show what I'm seeing.

Clearly a problem is occurring in #7 but it isn't one I'm running into (see this video) + this and the e2e test mentioned in #5 demonstrate that "Handl[ing] media image fields on page data form" currently works.

The error in #6 looks like it's coming from OpenAPI validation, which should obviously be addressed. If anyone currently experiencing it can either update this issue summary or create a new issue targeting that specific bug