Sören Rifé

Add OpenAPI example factories

3

Nowadays, the Sanic OpenAPI extension does not permit to add example requests and responses to your documented views. I suggest to add a field `example` to [definitions.Response](https://github.com/sanic-org/sanic-ext/blob/2d5e31334565bf8b68d345caf650fab66c0cfd2d/sanic_ext/extensions/openapi/definitions.py#L98), [definitions.RequestBody](https://github.com/sanic-org/sanic-ext/blob/2d5e31334565bf8b68d345caf650fab66c0cfd2d/sanic_ext/extensions/openapi/definitions.py#L130) and [definitions.Parameter](https://github.com/sanic-org/sanic-ext/blob/2d5e31334565bf8b68d345caf650fab66c0cfd2d/sanic_ext/extensions/openapi/definitions.py#L189)...