[REQ] Turn ExampleGenerator into a interface and allow an Codegen implementation to use its own example generator

Is your feature request related to a problem? Please describe.

Currently, an instance of ExampleGenerator is being used by the DefaultCodegen class.
Specific generators cannot change this because is fixed type in hardcoded. To change the behavior it would be necessary to override an ultra big method: fromOperation() . it is a too hard path.

Describe the solution you'd like

• My idea is to turn the ExampleGenerator class into an Interface and then to create a DefaultExampleGenerator class implementing it.

• DefaultCodegen has two different places whe examples a being created: handleMethodResponse, fromOperation and toExampleValue. I think that we could converhe those uses into the ExampleGenerator interface.

Describe alternatives you've considered

Additional context

Start by reading ExampleGenerator and DefaultCodegen, focusing on handleMethodResponse, fromOperation, and toExampleValue, where the issue says examples are created. Trace how DefaultCodegen currently uses ExampleGenerator and how generator-specific implementations could supply their own behavior. Done means the example-generation contract supports custom implementations without overriding fromOperation.