Log request and response headers

[JunTaoLuo]

Item 2 of #4.

cc @CesarBS @halter73

[JunTaoLuo]

Possibly need eventids or something more than just a string

[JunTaoLuo]

I thought it was best to log the headers and such closer to when they are actually read and written but I suppose when the HttpContext was created/disposed is good enough. I'll close this PR and open a new one in Hosting and remove the logging of headers in WebListener.

[halter73]

@davidfowl I think it would be a good idea to expose a connection and request ID via the IHttpConnectionFeature and IHttpRequestFeature respectively. This should make it easier to correlate logs from different layers. I can open issues in Abstractions and Kestrel if you agree.

[davidfowl]

IHttpConnectionFeature.ConnectionId I agree with but I don't think there should be a request id on the IHttpRequestFeature. I prefer what we have right now as it doesn't need to be implemented in the sever itself and it's not required for anything to function.

[Tratcher]

I expect we'll need ConnectionId at some point. We already have IHttpRequestIdentifierFeature for request id. I agree that it would make correlation easier if the Kestrel implemented IHttpRequestIdentifierFeature. WebListener does.