Use new ASP.NET Core environment variable

Just found that it is necessary to update Orleans doc Kubernetes hosting - .NET | Microsoft Learn
It sets old .NET Framework environment variable DOTNET_SHUTDOWNTIMEOUTSECONDS
Please see https://learn.microsoft.com/en-us/aspnet/core/fundamentals/host/generic-host?view=aspnetcore-9.0#settings-for-all-app-types

Author: oleksandr-bilyk

docs/orleans/deployment/kubernetes.md

@@ -99,7 +99,7 @@ spec:
             valueFrom:
               fieldRef:
                 fieldPath: status.podIP
-          - name: DOTNET_SHUTDOWNTIMEOUTSECONDS
+          - name: ASPNETCORE_SHUTDOWNTIMEOUTSECONDS # See .NET Generic Host in ASP.NET Core ShutdownTimeout https://learn.microsoft.com/en-us/aspnet/core/fundamentals/host/generic-host?view=aspnetcore-9.0#shutdowntimeout
             value: "120"
           request:
             # Set resource requests