JSON fields in content types - Improve the overall story

[sneridagh]

It is quite common to use in Volto content type fields that are stored in JSON using JSONField field type. This is useful to store structured data (as in the old Datagridfield). We would like to be able to apply the some of the transforms in that data structures, and being able to process resolveIds and image scales, etc in there too, like in the blocks.

Also, being able to apply them in a "smart" way, so that transforms apply to some fields that are marked as so. For example, we have a small use case working in the blocks transforms already:

{
  "blocks": {
    "asdadasd": {
      "@type": "URL",
       "value": "https://myserver/foo/bar"
    }
  }
}

but it would be great to expand this to other use cases, like images or for text indexing.

See also: plone/volto#2252