update docs: desribe link entry for regex redirects

docs/30_⚙️_Configuration.md

@@ -28,9 +28,9 @@ Let's start with an example for a `redirects_<FQDN>.json`:
     },
 
     "regex":{
-        "^/$":      {"code": 307, "target": "https://www.iml.unibe.ch" },
-        "^/ax.l.*": {"code": 307, "target": "https://www.axel-hahn.de" },
-        ".*":       {"code": 301, "target": "https://www2.example.com" }
+        "^/$":      {"code": 307, "target": "https://www.iml.unibe.ch", "link": "/"         },
+        "^/ax.l.*": {"code": 307, "target": "https://www.axel-hahn.de", "link": "/axelhahn" },
+        ".*":       {"code": 301, "target": "https://www2.example.com", "link": "/testme"   }
     }
 }
 ```
@@ -72,6 +72,7 @@ Both redirect section contain a redirect definition
 
 * code - http status code for redirection
 * target - target url of the redirect
+* link - optional, for regex only: set a path for a test link
 
 Status codes