docs(destination): destination services can be offered in multiple regions

Fixes https://git.fitko.de/fit-connect/api/-/issues/86

docs/getting-started/receiving/destination.mdx

@@ -70,7 +70,7 @@ $ curl \
           "schemaUri": "https://schema.fitko.de/fim/s00000000009_1.0.0.schema.json",
           "mimeType": "application/json"
         ],
-        "region": "DE13441111"
+        "regions": ["DE13441111"]
       }
     ],
     "callback": "https://example.com/callback",