mod_session: Introduce SessionExpiryUpdateInterval which allows to

configure the session/cookie expiry's update interval. PR 57300.

Submitted by: Paul Spangler <paul.spangler ni.com>
Reviewed/Committed by: ylavic


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1709121 13f79535-47bb-0310-9956-ffa450edef68