Add string format:"json-pointer" to statementPointerTarget property

[kd-ods]

Summary

To validate the basic format of the statementPointerTarget property in the Annotations object, we should add the string format: "json-pointer".

Additional context and details

The property is currently defined in the Statement.json file as:

        "statementPointerTarget": {
          "title": "Statement Fragment Pointer",
          "description": "An RFC6901 JSON Pointer (https://tools.ietf.org/html/rfc6901) describing the target fragment of the statement that this Annotation applies to, starting from the root of the Statement. An empty string (\"\") indicates that the Annotation applies to the whole Statement.",
          "type": "string"
        }