Make lookup-request config naming consistent with lookup-response configuration

[davidradl]

#193 changes add new custom format options for responses, the naming of the config options for lookup-response follows the standard Flink Kafka connector. The existing lookup-request does not follow the standard naming. It would make sense to amend the code in this area to use the proper naming convention. lookup-request.format.json.fail-on-missing-field should be lookup-request.json.fail-on-missing-field