Collect AKS attach rate numerator (Azure#37123)

* Fix a todo

* Remove space

Co-authored-by: Trask Stalnaker <[email protected]>

* Fix test

---------

Co-authored-by: Trask Stalnaker <[email protected]>

Author: heyams

sdk/monitor/azure-monitor-opentelemetry-exporter/src/main/java/com/azure/monitor/opentelemetry/exporter/implementation/statsbeat/AttachStatsbeat.java

@@ -76,8 +76,8 @@ static String initResourceProviderId(
                 } else {
                     return UNKNOWN_RP_ID;
                 }
-            case RP_AKS: // TODO will update resourceProviderId when cluster_id becomes available from the
-                // AKS AzureMetadataService extension.
+            case RP_AKS:
+                return envVarFn.apply("AKS_ARM_NAMESPACE_ID");
             case UNKNOWN:
                 return UNKNOWN_RP_ID;
         }

sdk/monitor/azure-monitor-opentelemetry-exporter/src/test/java/com/azure/monitor/opentelemetry/exporter/implementation/statsbeat/AttachStatsbeatTest.java

@@ -73,8 +73,10 @@ public void testFunctionsResourceProviderId() {
 
     @Test
     public void testAksResourceProviderId() {
-        assertThat(AttachStatsbeat.initResourceProviderId(ResourceProvider.RP_AKS, null, key -> null))
-            .isEqualTo("unknown");
+        Map<String, String> envVars = new HashMap<>();
+        envVars.put("AKS_ARM_NAMESPACE_ID", "test_aks_rp_id");
+        assertThat(AttachStatsbeat.initResourceProviderId(ResourceProvider.RP_AKS, null, envVars::get))
+            .isEqualTo("test_aks_rp_id");
     }
 
     @Test