[Data Object Editor] Data format for manyToManyRelation

[markus-moser]

Here an example:

 [
    {
      id: 35,
      type: 'asset',
      subType: 'image',
      published: true,
      fullPath: '/Car Images/buick/buick-1400243.jpg'
    },
    {
      id: 772,
      type: 'data-object',
      subType: 'News',
      published: true,
      fullPath: '/News/Lor separat existentie es un myth'
    },
]

The subtype should be either the class name of it is a concrete data object or the type attribute of the element's class (so e.g. image, document, folder etc.).

If you prefer we can also name/handle the attributes a bit different but this is the data which we need.

Part of #566