Visual Editing backend supports adding a new choice field

The backend should support the possibility to create a new choice field. For this purpose we should add a new endpoint:

POST documents/{documentId}/editable/{fieldPath}[_<order>_]/<type>

Where the order is an unsigned numeric value corresponding to a one-based index. By default, it equals 1, and the value will be inserted into the beginning.

And the type corresponds to the choice field type. For example,

POST documents/uuid/editable/hap:venue[3]/hap:realestate