Support keep-alive options for incoming requests

[kjellmorten]

Node offers some keep-alive options on an http server, and especially the keepAliveTimeout is important, to avoid incoming connections being closed too soon.

We should make at least keepAliveTimeout available on the incoming options object.

References:

• https://nodejs.org/api/http.html#httpcreateserveroptions-requestlistener
• https://connectreport.com/blog/tuning-http-keep-alive-in-node-js/