Use ImageWidget for Teaser override image

[rotavio]

Is your feature request related to a problem? Please describe.
Regarding issue 4286, I'm trying to use the new Image Widget for the override image on the Teaser block. I think it would be nice if the user could also upload a new image, instead of being limited to the ones already saved as content.

Describe the solution you'd like
Use the ImageWidget instead of ObjectBrowser Widget

Describe alternatives you've considered
I`ve tried to replace it, but for some reason the image saved is only a string with the image url, not the full object with image_scales, expected by the teaser view

[ichim-david]

@rotavio I have made such a change as part of this pull request #6156
as I've mentioned in this comment #6156 (comment)

I have however reverted the commit since there was no feedback that we want todo this at this moment
although to be fair I didn't ask if we want such a thing either.

If there is consent from the @plone/volto-team we can always make a new pull request with such a feature.