Add middleware that closes connections on responses to Connection: close header

[samsondav]

If we respond to a request with Connection: close, we should send a response with Connection: close and then close it ourselves.

This works around buggy clients that send Connection: close and never close the connection themselves.

[CrowdHailer]

Closing this issue as behaviour of connection header depends on transport layer. HTTP/1.1 vs HTTP/2