Update prod-config.json

Author: abuabraham-ttd

scripts/gcp-oidc/conf/prod-config.json

@@ -13,6 +13,7 @@
   "optout_api_uri": "https://optout.uidapi.com/optout/replicate",
   "optout_s3_folder": "optout-v2/",
   "identity_token_expires_after_seconds": 259200,
+  "uid_instance_id_prefix": "unknown",
   "runtime_config_store": {
     "type": "http",
     "config" : {