[RulesetEng, Workers] Add note about metro code values (cloudflare#26655)

Author: pedrosousa

src/content/docs/workers/runtime-apis/request.mdx

@@ -309,7 +309,9 @@ All plans have access to:
 
 * `metroCode` string | null
 
-  * Metro code (DMA) of the incoming request, for example, `"635"`.
+  * Metro code (DMA) of the incoming request.
+
+    Currently `metroCode` is not populated, but this may change in the future. Refer to the [Changelog](/changelog/) for any updates.
 
 * `region` string | null
 

src/content/fields/index.yaml

@@ -209,8 +209,8 @@ entries:
     categories: [Request, Geolocation]
     keywords: [request, location, geolocation, dma, client, visitor]
     summary: The metro code or Designated Market Area (DMA) code associated with the incoming request.
-    example_value: |-
-      "635"
+    description: |-
+      **Note**: Currently the value of `ip.src.metro_code` is always `"0"`, but this may change in the future. Refer to the [Changelog](/changelog/) for any updates.
 
   - name: ip.src.region
     data_type: String