[IMP] web: make date widget work with datetime field

Task-3698841

closes odoo/documentation#10325

Related: odoo/odoo#161705
Related: odoo/enterprise#67258
Signed-off-by: Mathieu Duckerts-Antoine (dam) <dam@odoo.com>

content/developer/reference/frontend/javascript_reference.rst

@@ -707,6 +707,14 @@ Date & Time (`datetime`)
 
             <field name="datetimefield" options="{'rounding': 10}" />
 
+    - `show_time`: when set to false, it hides the time part from the datetime field.
+      The field will still accept datetime values, but the time part will be hidden in
+      the UI (default: `true`).
+
+        .. code-block:: xml
+
+            <field name="datetimefield" widget="datetime" options="{'show_time': false}" />
+
 Date Range (`daterange`)
     This widget allows the user to select start and end date from a single picker.