proxy: add experimental async mode

example/config.jsonc

@@ -38,5 +38,13 @@
             "exclude_regex": ".*/commit/.*",
             "action_on_exclude": "DENY"
         }
-    ]
+    ],
+
+    // experimental settings. Use with caution!
+    "experimental": {
+        // If enabled, all requests to the proxy will create their own thread.
+        // this can increase the throughput of the proxy, especially when there are a lot of requests made
+        // all at once.
+        "async_proxy": false
+    }
 }