[Codegen] Add hasDefaultResponse property

[aymanbagabas]

Check if there's a default response in specs

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[aymanbagabas]

Used in #8515

@4brunu @wing328

[4brunu]

I don't have much knowledge of CodegenOperation.java so let's wait for the @wing328 review.

[wing328]

cc @OpenAPITools/generator-core-team

[wing328]

Looks good to me.

[PirvuCatalin]

Is this actually working? I cannot specify this value, what type of property? Documentation is also not updated... More details, would you?