Allow common headers on Blueprint/MethodView

[Petr-Pan]

Hi,

I'd like to propose an option to define header schemas on a Blueprint or at least MethodView level.

An example use case would be a context/correlation id - optional headers in the request, whose values can then be used for easier tracking/debugging purposes in logs.

Currently, if I'm not mistaken, to auto-document these, one has to decorate every single endpoint of the API, which is a bit cumbersome and error-prone.