Add admin settings for the Calendar Trash bin

Closes #7696

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

admin_manual/groupware/calendar.rst

@@ -76,6 +76,19 @@ If you need to allow this, change the following parameter to::
 
  php occ config:app:set dav webcalAllowLocalAccess --value yes
 
+Trash bin
+---------
+
+Nextcloud supports a calendar, events and tasks trash bin.
+
+The default delay before objects are purged from the trash bin is of 30 days. A backgroup job runs every 6 hours to cleanup expired objects.
+
+To set up a different retention period, change the ``calendarRetentionObligation`` option::
+
+ php occ config:app:set dav calendarRetentionObligation --value=2592000
+
+Where the value is the number of seconds for the period. Setting the value to ``0`` disables the trash bin.
+
 Resources and rooms
 -------------------
 

user_manual/groupware/calendar.rst

@@ -225,7 +225,7 @@ You can also tell when the recurrence ends.
 Trash bin
 ~~~~~~~~~
 
-If you delete events, tasks or a calendar in Calendar, your data won't be gone yet. Instead, those items will be collected in a *trash bin*. This offers you to undo a deletion. After a period of 30 days those items will be deleted permanently. You can also permanently delete earlier if you wish.
+If you delete events, tasks or a calendar in Calendar, your data won't be gone yet. Instead, those items will be collected in a *trash bin*. This offers you to undo a deletion. After a period which defaults to 30 days (your administrator may have changed this setting), those items will be deleted permanently. You can also permanently delete earlier if you wish.
 
 .. figure:: images/calendar_trash_bin.png