Fix waitforexecution property not being taken into account by default_search

1. Following to NXS-3474, I tried to manually set up the following properties with:

   <require>org.nuxeo.search.ui.contentviews</require>
   
   <extension point="contentViews" target="org.nuxeo.ecm.platform.ui.web.ContentViewService">
   
       <contentView name="default_search">
           <waitForExecution>true</waitForExecution>
           <waitForExecutionSentence>my custom sentence</waitForExecutionSentence>
       </contentView>
     
   </extension>
   

   This does not work and only waitForExecution property is taken into account.
   This may also be related to bug NXP-19898 where the default_search is behaving oddly when overloaded.

As a workaround, customer can use the above contribution for the waitForExecution property and overload the label.search.waitForExecution label defined by default in the default_search content view.