Ship a JSON editor component to be used in ui:schema

If a user wants a text field to be edited as JSON, she could use it to enhance the fields.

We don't want to ship it in rjsf so this could be done here in kinto-admin

Start by tracing the existing ui:schema implementation and the field components it uses; the issue names no specific files or tests. Clarify the JSON editor’s expected editing behavior and how it should be exposed through ui:schema. Done means the component is available for text fields configured as JSON without being shipped in rjsf.

Written by the indexing model from the issue text.