fix SyncTrigger URL of the BuildService (#7370)

Author: TsuyoshiUshio

src/WebJobs.Script.WebHost/Management/FunctionsSyncManager.cs

@@ -561,7 +561,13 @@ internal HttpRequestMessage BuildSetTriggersRequest()
             var url = default(string);
             if (_environment.IsKubernetesManagedHosting())
             {
-                url = $"http://{ManagedKubernetesBuildServiceName}.{ManagedKubernetesBuildServiceNamespace}.svc.cluster.local:{ManagedKubernetesBuildServicePort}/operations/settriggers";
+                var buildServiceHostname =
+                    _environment.GetEnvironmentVariable("BUILD_SERVICE_HOSTNAME");
+                if (string.IsNullOrEmpty(buildServiceHostname))
+                {
+                    buildServiceHostname = $"http://{ManagedKubernetesBuildServiceName}.{ManagedKubernetesBuildServiceNamespace}.svc.cluster.local:{ManagedKubernetesBuildServicePort}";
+                }
+                url = $"{buildServiceHostname}/api/operations/settriggers";
             }
             else
             {

test/WebJobs.Script.Tests.Integration/Management/FunctionsSyncManagerTests.cs

@@ -657,13 +657,14 @@ public void Use_Website_Name_If_Website_Hostname_Is_Not_Available(string hostNam
         }
 
         [Theory]
-        [InlineData("KUBERNETES_SERVICE_HOST", "http://k8se-build-service.k8se-system.svc.cluster.local:8181/operations/settriggers")]
+        [InlineData("KUBERNETES_SERVICE_HOST", "http://k8se-build-service.k8se-system.svc.cluster.local:8181/api/operations/settriggers")]
         [InlineData(null, "https://appname.azurewebsites.net/operations/settriggers")]
         public void Managed_Kubernetes_Environment_SyncTrigger_Url_Validation(string kubernetesServiceHost, string expectedSyncTriggersUri)
         {
             _mockEnvironment.Setup(p => p.GetEnvironmentVariable(EnvironmentSettingNames.KubernetesServiceHost)).Returns(kubernetesServiceHost);
             _mockEnvironment.Setup(p => p.GetEnvironmentVariable(EnvironmentSettingNames.PodNamespace)).Returns("POD_NAMESPACE");
-
+            _mockEnvironment.Setup(p => p.GetEnvironmentVariable("BUILD_SERVICE_HOSTNAME"))
+                .Returns("");
             var httpRequest = _functionsSyncManager.BuildSetTriggersRequest();
             Assert.Equal(expectedSyncTriggersUri, httpRequest.RequestUri.AbsoluteUri);
             Assert.Equal(HttpMethod.Post, httpRequest.Method);