fix: opium is built on top of the httpaf platform (#6147)

frameworks/OCaml/httpaf/benchmark_config.json

@@ -13,7 +13,7 @@
         "language": "OCaml",
         "flavor": "None",
         "orm": "None",
-        "platform": "None",
+        "platform": "httpaf",
         "webserver": "None",
         "os": "Linux",
         "database_os": "Linux",

frameworks/OCaml/opium/benchmark_config.json

@@ -22,7 +22,7 @@
         "database_os": "Linux",
         "display_name": "opium",
         "notes": "",
-        "versus": "None"
+        "versus": "httpaf"
       },
       "haproxy": {
         "json_url": "/json",
@@ -45,7 +45,7 @@
         "database_os": "Linux",
         "display_name": "opium-haproxy",
         "notes": "",
-        "versus": "None"
+        "versus": "httpaf"
       }
   }]
 }