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 30 days. A background job runs every 6 hours to clean up 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

@@ -223,7 +223,7 @@ 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 is not 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 administration may have changed this setting), those items will be deleted permanently. You can also permanently delete items earlier if you wish.
 
 .. figure:: images/calendar_trash_bin.png