Reduce impact of periodic item expiry on front-end ops

The frequency at which the expiry pager runs can be set using a configuration parameter exp_pager_stime. It has a default of 3600s, which means it is configured to run once an hour.

The default has been unchanged since at least version 2.5.1.

There have been customer issues (see linked CBSEs) where expiry has impacted front-end operations. Therefore there may be benefit in reducing the default from 1 hour to something smaller e.g. 10 minutes.

It looks like the previous approach to the problem of the expiry affecting front-end ops has been to introduce a schedule start time to ensure that expiry happened at a quiet time.