Support global custom operationId generation hook

[siyb]

Currently, the operationId is created in the following manner:

operationId: "MyController.getMyMethod"

When creating OpenAPI bindings using @openapitools/openapi-generator-cli this will result in the following client method:

MyApi.myControllerGetMyMethod()

So it would be nice if there were a way to provide a custom operationId generator to be able to adjust the operationId globally and not just per method.