expose prometheus exporter for test

Author: dashpole

samples/instrumentation-quickstart/otel-collector-config.yaml

@@ -111,6 +111,14 @@ processors:
     detectors: ["env", "gcp"]
 
 service:
+  telemetry:
+    metrics:
+      readers:
+        - pull:
+            exporter:
+              prometheus:
+                host: '0.0.0.0'
+                port: 8888
   pipelines:
     traces:
       receivers: ["otlp"]