Return `Accept` header when `Bad Content Type` is reported...

According to HTTP standard, when "Bad content type" is reported, we should send a list of accepted content types for the given address in `Accept` header.
This could be realized by a walk over the type with a given path.

This allows for content negotiation and speeds up debugging expectations of API servers:
https://developer.mozilla.org/en-US/docs/Web/HTTP/Content_negotiation#the_accept_header