Merge pull request #1867 from OpenTechFund/fix/datetime-widget-placeholder-format-correction

Correct the datetime template placeholder to ISO standard date format.

hypha/templates/django/forms/widgets/datetime.html

-<input type="datetime-local" placeholder="dd/mm/yyyy hh:mm" name="{{ widget.name }}"{% if widget.value != None %} value="{{ widget.value|stringformat:'s' }}"{% endif %}{% include "django/forms/widgets/attrs.html" %} />
+<input type="datetime-local" placeholder="yyyy-mm-dd hh:mm" name="{{ widget.name }}"{% if widget.value != None %} value="{{ widget.value|stringformat:'s' }}"{% endif %}{% include "django/forms/widgets/attrs.html" %} />