Fix elasticsearch query ecm:path STARTSWITH "/" returning placeless documents

When you have a placeless document, it is returned by a page provider plugged on elastic search with a ecm:path STARTSWITH "/" clause despite its path is avatar.jpeg (not /avatar.jpeg).

Note that a page provider not plugged on es does not return it which is inconsistent anyway.

Steps to repoduce:

• in jsf ui, create an avatar.jpeg document wherever you want.
• publish a PDF rendition to a section
• https://nightly.nuxeo.com/nuxeo/api/v1/search/pp/nxql_search/execute?queryParams=SELECT%20*%20FROM%20DOCUMENT%20WHERE%20dc:title=%22avatar.jpeg%22%20AND%20ecm:path%20STARTSWITH%20%22/%22 does not return a placeless doc OK
• https://nightly.nuxeo.com/nuxeo/api/v1/search/pp/domain_documents/execute?currentPageIndex=0&offset=0&pageSize=16&queryParams=%2F returns a placeless doc KO

Note that domain_documents page provider
is plugged on elasticsearch,

Root cause is makeStartsWithQuery which just does not take into account placeless documents:

        if ("/".equals(value)) {
            // match all document with a path
            filter = QueryBuilders.existsQuery(indexName);
        }