Add JacksonJsonPointerValueLocator to locate a value not on the top level.

[dmikurube]

See a sample usage below.

Response:

{
  "foo": {
    "bar": {
      "id": 123
    }
  }
}

Building ServiceResponseSchema to read that 123.

        JacksonServiceResponseSchema.builder()
            // Reading "/foo/bar/id" as Embulk's column "id".
            .add(new JacksonJsonPointerValueLocator("/foo/bar/id"), "id", Types.LONG)
        ...