Add crawler_duration gauge and server_queries counter

internal/handlers.go

@@ -231,6 +231,8 @@ func (s *Server) SearchHandler() httprouter.Handle {
 		ctx.Results = results
 		ctx.SearchTook = searchResults.Took.Truncate(time.Nanosecond)
 
+		metrics.Counter("server", "queries").Inc()
+
 		s.render("search", w, ctx)
 	}
 }