TT-16229 update tyk.conf example (#7603)

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### Ticket Details

<details>
<summary>
<a href="https://tyktech.atlassian.net/browse/TT-16229" title="TT-16229"
target="_blank">TT-16229</a>
</summary>

|         |    |
|---------|----|
| Status  | In Code Review |
| Summary | [Innersource] Default secure for new XFF depth config |

Generated at: 2025-12-05 13:04:25

</details>

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Author: sedkis

tyk.conf.example

@@ -32,6 +32,7 @@
     "allow_explicit_policy_id": true
   },
   "http_server_options": {
+    "xff_depth": 1,
     "enable_strict_routes": true,
     "enable_path_prefix_matching": true,
     "enable_path_suffix_matching": true