Add IdleConnTimeout to Traefik's http.server settings (#1340)

* Add IdleTimeout setting to http.server

Without such a timeout there is a risk of resource leakage from piling up connections, particularly when exposing Traefik to the Internet.

Set the default to be 180 seconds

* Add IdleConnTimeout to Traefik's http.server settings

Without enforcing a timeout Traefik is susceptible to resource leakage, particularly when deployed as a public facing proxy exposed to the Internet.

Set the default to be 180 seconds

* tweak

* Update configuration.go

* add some documentation for the idletimeout setting

* need to cast idletimeout

* update doc to refect format specifics

docs/user-guide/examples.md

@@ -130,4 +130,11 @@ defaultEntryPoints = ["http"]
     headerField = "X-WebAuth-User"
     [entryPoints.http.auth.basic]
     users = ["test:$apr1$H6uskkkW$IgXLP6ewTrSuBkTrqE8wj/", "test2:$apr1$d9hr9HBB$4HxwgUir3HP4EsggP/QNo0"]
-```
+```
+
+## Override the Traefik HTTP server IdleTimeout and/or throttle configurations from re-loading too quickly
+
+```
+IdleTimeout = "360s"
+ProvidersThrottleDuration = "5s"
+```