Returns the duration of time which this connection can be safely kept
idle. If the connection is left idle for longer than this period of time,
it MUST not reused. A value of 0 or less may be returned to indicate that
there is no suitable suggestion.
When coupled with a ConnectionReuseStrategy, if
HttpResponse, HttpContext) returns true, this allows you to control
how long the reuse will last. If keepAlive returns false, this should
have no meaningful impact