feat: add response time histogram metric

doc/fr/references/metrics.md

@@ -24,31 +24,6 @@ Chaque layer associé à un proxy peut également ses propres métriques spécif
     bouncer_proxy_director_proxy_requests_total{proxy="cadoles"} 64
     ```
 
-#### `bouncer_proxy_director_proxy_responses_duration_seconds{proxy=<proxyName>}`
-
-- **Type:** `histogram`
-- **Description**: Histogramme du temps de traitement du cycle requête/réponse par proxy
-- **Exemple**
-
-  ```
-  # HELP bouncer_proxy_director_proxy_responses_duration_seconds Bouncer proxy responses duration
-  # TYPE bouncer_proxy_director_proxy_responses_duration_seconds histogram
-  bouncer_proxy_director_proxy_responses_duration_seconds_bucket{proxy="dummy",le="0.005"} 13
-  bouncer_proxy_director_proxy_responses_duration_seconds_bucket{proxy="dummy",le="0.01"} 13
-  bouncer_proxy_director_proxy_responses_duration_seconds_bucket{proxy="dummy",le="0.025"} 13
-  bouncer_proxy_director_proxy_responses_duration_seconds_bucket{proxy="dummy",le="0.05"} 13
-  bouncer_proxy_director_proxy_responses_duration_seconds_bucket{proxy="dummy",le="0.1"} 13
-  bouncer_proxy_director_proxy_responses_duration_seconds_bucket{proxy="dummy",le="0.25"} 13
-  bouncer_proxy_director_proxy_responses_duration_seconds_bucket{proxy="dummy",le="0.5"} 13
-  bouncer_proxy_director_proxy_responses_duration_seconds_bucket{proxy="dummy",le="1"} 13
-  bouncer_proxy_director_proxy_responses_duration_seconds_bucket{proxy="dummy",le="2.5"} 13
-  bouncer_proxy_director_proxy_responses_duration_seconds_bucket{proxy="dummy",le="5"} 13
-  bouncer_proxy_director_proxy_responses_duration_seconds_bucket{proxy="dummy",le="10"} 13
-  bouncer_proxy_director_proxy_responses_duration_seconds_bucket{proxy="dummy",le="+Inf"} 13
-  bouncer_proxy_director_proxy_responses_duration_seconds_sum{proxy="dummy"} 0.009556884
-  bouncer_proxy_director_proxy_responses_duration_seconds_count{proxy="dummy"} 13
-  ```
-
 ### Serveur d'administration
 
 _Pas de métrique supplémentaire._