code: public static String getDocumentLink(final String databaseName, final String collectionName, final String documentId) {
          return getCollectionLink(databaseName, collectionName) + "/docs/" + documentId;
      }
docs: Gets document link.
  
  @param databaseName   the database name
  @param collectionName the collection name
  @param documentId     the document id
  @return the document link