Fix time search filter in OAI harvester configuration

[koplas]

Specifying the time range results in an error as the backend expects an ISO formatted date.

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[josegar74]

Tested and works, the following error does not longer happens:

2025-09-16T15:59:33,345 ERROR [geonetwork.domain] - Error parsing ISO DateTimes 'Tue Sep 16 2025 00:00:00 GMT+0200 (Central European Summer Time)'. Error is: Text 'ue Sep 16 2025 00:00:00 GMT+0200 (Central European Summer Time)' could not be parsed at index 0
java.time.format.DateTimeParseException: Text 'ue Sep 16 2025 00:00:00 GMT+0200 (Central European Summer Time)' could not be parsed at index 0

But after saving the form, refreshing the form doesn't display the values selected in the UI, it displays the date selectors without a selected date.

[koplas]

But after saving the form, refreshing the form doesn't display the values selected in the UI, it displays the date selectors without a selected date.

I currently don't have a quick fix for this. In a week I should have time to investigate this.