no way to set `operationId` to the operation object

see here 
https://github.com/OAI/OpenAPI-Specification/blob/master/versions/2.0.md#operation-object

It is not mandatory but It actually required if you want to deploy on GCP see here 
https://cloud.google.com/endpoints/docs/openapi/configure-endpoints#operationid

As a solution please just add a field for to set a value. 
The uniqueness can be left to the user to take care of.

Thanks. 