[FR] Add support for pulling values from a nested entry in a CKEditor field (similar to Matrix sub fields)

[rungta]

Now that CKEditor has baked in support for nested entries which are full-blown elements, similar to the erstwhile Matrix blocks, it'll be useful to specify using field values from nested entries for the SEO values.

Eg: We have a CKEditor field body which supports a few nested entry types (image, video, etc) and we’d like to pull in the first image from the body field to be used as the SEO image. Sticking with the existing matrix field syntax, this could perhaps be expressed as:

'image' => ['seoImage', 'mainImage', 'body.image:assetField']

What do you think?