add an example of a search with a page provider using several aggregates in REST API 'search' endpoint documentation

  <extension target="org.nuxeo.ecm.core.schema.TypeService" point="doctype">
    <doctype name="testcase_pp" extends="Document">
      <facet name="ContentViewDisplay"/>
      <facet name="SavedSearch"/>
      <facet name="HiddenInNavigation"/>
      <schema name="testcase_pp"/>
    </doctype>
  </extension>

  <extension target="org.nuxeo.ecm.platform.query.api.PageProviderService" point="providers">
    <genericPageProvider class="org.nuxeo.elasticsearch.provider.ElasticSearchNxqlPageProvider" name="testcase">
      <property name="coreSession">#{documentManager}</property>
      <whereClause>
        <fixedPart>ecm:mixinType != 'HiddenInNavigation' AND ecm:isCheckedInVersion = 0 AND ecm:currentLifeCycleState != 'deleted'</fixedPart>
      </whereClause>
      <searchDocumentType>testcase_pp</searchDocumentType>
      <aggregates>
        <aggregate id="dublincore_source_agg" type="terms" parameter="dc:source">
          <field schema="testcase_pp" name="dublincore_source_agg"/>
          <properties>
            <property name="order">term asc</property>
          </properties>
        </aggregate>
        <aggregate id="dublincore_rights_agg" type="terms" parameter="dc:rights">
          <field schema="testcase_pp" name="dublincore_rights_agg"/>
          <properties>
            <property name="order">term asc</property>
          </properties>
        </aggregate>
      </aggregates>
      <pageSize>10</pageSize>
    </genericPageProvider>
  </extension>