Allow passing label-values to call-with-duration-metric

prometheus.scm

@@ -361,6 +361,7 @@ values are the values."
                                     (buckets %default-histogram-buckets)
                                     docstring
                                     (labels '())
+                                    (label-values '())
                                     (label-preset-values '()))
   "Call @var{thunk} while recording the duration in seconds between
 calling @var{thunk} and the procedure ending using a metric by the
@@ -382,7 +383,9 @@ The metric with the name @var{metric-name} is fetched from the
     (call-with-values
         thunk
       (lambda results
-        (metric-observe metric (- (current-time) start-time))
+        (metric-observe metric
+                        (- (current-time) start-time)
+                        #:label-values label-values)
 
         (apply values results)))))