Fix documentation in the widget type definition

According to this link the default start and end time for a Date Range widget should be 00:00 and 23:59.
This is misleading and is also not working when using a pattern like yyyy-MM-dd HH:mm in the Format field of the widget. (see wrongSettings.png)
After further checking the definition, formats used for default times are like

<property name="startDefaultTime">00:00:00</property>
<property name="endDefaultTime">23:59:59</property>

So using a pattern like yyyy-MM-dd HH:mm:ss does indeed work (see correctSettings.png) and triggers time auto-completion in the search field (see timeSearch.png).
As a final result this generates the correct query to Elasticsearch.

To fix this, the documentation should mention :
Defaults to 23:59:59, available since 7.1.
and
Defaults to 00:00:00, available since 7.1.