OpenApi: Do not use ArrayNode to store parameters

We are using ArrayNode to store parameters. We use it only as a List which stores parameter names. Do not use ArrayNode as addPath (et. al) method parameter for parameters and use List instead. In addition, create dedicated Java class to store parameters as described in https://swagger.io/specification/#parameter-object and use it in Operation.java. Along the way we will also eliminate OperationBuilder#getTypeParentNode method.