config: add token_valid_for

example/config.jsonc

@@ -81,5 +81,8 @@
 
         // Where to save the logfile. Each run will continue appending to this file. It may grow HUGE! No automatic pruning / compression is done.
         "traffic_log_file": "./traffic.csv"
-    }
+    },
+
+    // how long the token (solved challenge) should be valid for before showing a new challenge, in minutes
+    "token_valid_for": 60 // 1 hour
 }