Provide setting for slidingExpiration time.

Currently this appears to use the DistributedCache default slidingExpiration time (20 minutes).  If this expires in the store, the application breaks.  Would be nice to configure this for a much longer expiration without having to change the store default. 

e.g. 
{
   DataProtectionSlidingExpirationSeconds: 31536000 // 1 year
}