Make nuxeo-suggester customizable

Currently nuxeo-app.html contains

 <nuxeo-suggester id="suggester"></nuxeo-suggester>

which makes it impossible to override the suggest bar on top on the UI.

 Some customers are requesting to make changes with
 

1. replace the current code with a slot

   <nuxeo-slot name="DOCUMENT_SUGGESTER"></nuxeo-slot>
   

2. move these lines to a the nuxeo-suggester element

   <nuxeo-keys keys="/ ctrl+space s" on-pressed="_showSuggester"></nuxeo-keys>
   
   {
   _showSuggester(e) {    
      e.detail.keyboardEvent.preventDefault();
      this.$.suggester.toggle();  // Ajuster l'appel de fonction
   },

3. add a contribution for this new slot

   <nuxeo-slot-content name="documentSuggester" slot="DOCUMENT_SUGGESTER">  
     <template>    
       <nuxeo-suggester id="suggester"></nuxeo-suggester> 
     </template>
   </nuxeo-slot-content>