Storage Scale - Safe-guarded snapshots - allow expiration - give client to set its own expiration parameter in the GUI snapshot rule

By setting the "Allow Expiration" for snapshot rules under the GUI, it sets the snapshot only until the next execution, not for the whole retention, neither allows to client to sets its own retention.

Based on the IBM Documentation "https://www.ibm.com/docs/en/storage-scale/5.1.8?topic=systems-managing-snapshots-using-storage-scale-gui" :

- In the Retention fields, specify the number of snapshots that must be retained in a time period.

- Select the Allow Expiration checkbox to delete the snapshot when the defined retention period is completed.

The client has a snapshot policy which executes the snap multiple times a day (every 3 hours) and retain the last 6 versions of it. 

[root@xsscalensd01a ~]# /usr/lpp/mmfs/gui/cli/lssnaprule
Cluster       Name   Snapshot Prefix Frequency    Hours             DaysW DaysM Weeks Months Min after Exclude start Exclude end Max Hrs/Min Max days Max weeks Max months Last implemented  Off-hour deletions
GPFSLAB.CVALE policy @GMT            non periodic 04,10,13,16,19,22 N/A   ALL   N/A   ALL    05        N/A           N/A         6           0        0         0          11/30/23 10:00 AM no
 

When the snapshot of Nov 30 10:05 was taken, the expiration was set only to 3 hours later, meaning the next execution - Nov 30 13:05 

[root@xsscalensd01a ~]# mmlssnapshot DadosLab
Snapshots in file system DadosLab:
Directory                SnapId    Status  Created                   ExpirationTime            Fileset
@GMT-2023.11.30-13.05.22 13        Valid   Thu Nov 30 10:05:24 2023  Thu Nov 30 13:05:00 2023
 

However the snapshot retention was set to keep the last 6 executions of a 3-hour schedule, so the expiration should be set on the next 18 hours.

Also client wanted to be able to have more flexibility to choose for how long to keep it, in within the policy.  Once the "Allow Expiration" box was set, it could bring another field to the client determine - [  ] hours  [ ] days... and client could add the number of hours to retain, if it is under the retention period of the snapshot policy.