Bug 35191: Make entries per page configurable for items table on staff detail page

The new API driven items view defaults to 20 per page. This is a bit low, it would be great if it could be configurable to a higher value per the table configuration.

Test plan:
1. Apply this patch
2. restart_all (memcached restart is required)
3. Go to Administration > Table settings
4. Catalogue > holdings_table | otherholdings_table
=> Notice the new "Default display length"
5. Select something else than 20
6. Go to the detail page of a record with lot of records
=> Notice that the default value defined in the settings is used.

Signed-off-by: Emily Lamancusa <emily.lamancusa@montgomerycountymd.gov>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit 8e211a1fef)
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>

admin/columns_settings.yml

@@ -371,6 +371,7 @@ modules:
   catalogue:
     detail:
       holdings_table:
+        default_display_length: 20
         columns:
             -
               columnname: holdings_checkbox
@@ -437,6 +438,7 @@ modules:
               cannot_be_modified: 1
 
       otherholdings_table:
+        default_display_length: 20
         columns:
             -
               columnname: otherholdings_checkbox