Fix Prometheus config example (#5397)

Author: sfc-gh-vguttha

content/en/docs/collector/internal-telemetry.md

@@ -36,11 +36,11 @@ service:
   telemetry:
     metrics:
       readers:
-        pull:
-          exporter:
-            prometheus:
-              host: '0.0.0.0'
-              port: 8888
+        - pull:
+            exporter:
+              prometheus:
+                host: '0.0.0.0'
+                port: 8888
 ```
 
 You can adjust the verbosity of the Collector metrics output by setting the