Add copyright header to .editorconfig and update files (#13306)

.editorconfig

@@ -48,6 +48,8 @@ indent_size = 2
 # Sort using and Import directives with System.* appearing first
 dotnet_sort_system_directives_first = true
 
+file_header_template = Copyright (c) Microsoft Corporation.\nLicensed under the MIT License.
+
 # Modifier preferences
 csharp_preferred_modifier_order = public,private,protected,internal,static,extern,new,virtual,abstract,sealed,override,readonly,unsafe,volatile,async:suggestion
 

src/Microsoft.PowerShell.Commands.Utility/commands/utility/RunspaceAttribute.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
+// Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
 #pragma warning disable 1634, 1691

test/xUnit/csharp/test_CryptoUtils.cs

@@ -1,3 +1,6 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
 using System;
 using System.Management.Automation.Internal;
 using System.Text;