Ability to return a custom HTTPResponse as result of a validation inside the HTTPValidator response

[malcommac]

Feature Request

HTTPValidator responses include the ability to retry a call, fail the chain or move successfully to the next validator.
Sometimes you may want to slightly modify the received response by altering some values or return a custom subclass of the HTTPResponse with some data inside.

This involves some changes:

• The HTTPResponse struct becomes a class so we can inherit from it
• Some properties of the HTTPResponse must be marked as open
• HTTPValidator allows a new return value of HTTPResponseValidatorResult called nextValidatorWithResponse which allows to return a new HTTPResponse instance which is forwarded along any subsequent validator until the end.

The important change is the transformation to struct which implies changes from the memory management side.