Bug 37371: Move Maskito instantiation to onReady ( OPAC )

To test:
1. Find a any date picker in Koha, like DOB in the patron record.
2. Add a date, either manually or using the date picker.
3. Once there is a date like 07/15/2024 try to edit only part of the
   date, or the '15'.
4. The date easily becomes malformed.
5. APPLY PATCHSET, maybe clear your browser cache too
6. Try directly inputing dates. I would suggest the following places:

-Patron record DOB
-Specify due date on circ/circulation.pl as this includes time
-Add item screen, this is the dateaccessioned plugin
-OPAC self reg/self modify

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
(cherry picked from commit bae3203f70)
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>

koha-tmpl/opac-tmpl/bootstrap/en/includes/calendar.inc

@@ -102,15 +102,16 @@
                         instance.set('allowInput',false);
                     }
                 });
-        },
-        onOpen: function( selectedDates, dateText, instance ) {
-            var thisInput = instance.input;
-            let options = maskitoDateOptionsGenerator({
-                mode: altinput_dateformat,
-                separator: delimiter,
-            });
 
-            new Maskito( instance.altInput, options );
+                /* When flatpickr instance is ready, add maskito input mask */
+                var thisInput = instance.input;
+                let options = maskitoDateOptionsGenerator({
+                    mode: altinput_dateformat,
+                    separator: delimiter,
+                    overwriteMode: 'replace',
+                });
+
+                new Maskito( instance.altInput, options );
         },
         onClose: function( selectedDates, dateText, instance) {
             validate_date( dateText, instance );