Add config schema for field copy

The patch is incomplete:

- example of config for field copy:

id: spec_id_copy
label: 'Spec ID copy'
ui_limit: 'some_content_type|*'
type: display_field_copy
type_label: 'Copy field'
entities:
  node: node
properties:
  field_id: node.some_content_type.field_specification_id

- use example from DS on how to define schema for a field ./ds/config/schema/ds.field.schema.yml

I take it back - patch is complete and was ported to an MR. Thank you @diegopino for your contribution!

MR is good for review.