Feat/add response validation middleware

[zucchinho]

The OapiResponseValidator follows largely the same pattern as the OapiRequestValidator. A key difference is that the validation happens after the handler chain has been invoked, and it is obviously the response we are validating.

A wrapper around the underlying gin.ResponseWriter is needed to capture the response content. If the response is valid, it is written to the underlying writer.

In the case of bad responses, a 500 status code is returned.
If the route is not recognized, a 404 is returned.

Where feasible, common code is now shared between the 2 middlewares. This also facilitates creating a hybrid middleware which validates both requests and responses at some point in the future.

[zucchinho]

any chance of a review on this?

[jamietanna]

Will come back to it after the release of v2.2.0 for oapi-codegen, which should be next couple of days :)

[zucchinho]

Will come back to it after the release of v2.2.0 for oapi-codegen, which should be next couple of days :)

@jamietanna did the update to 2.2.0 go smoothly? i appear to acquired some conflicts here as a result, any use resolving these now or should i wait for v2 to stabilize?