Add Instruction to ensure Copyright header is present at start of script and module files (#27408)

.github/instructions/script-module-file-format.instructions.md

@@ -0,0 +1,27 @@
+---
+applyTo:
+  - "**/*.ps1"
+  - "**/*.psm1"
+---
+
+# Script and Module File Format
+
+These instructions define required file-level formatting for PowerShell scripts and module files in this repository.
+
+## Copyright Header
+
+If a change adds a new `.ps1` file or `.psm1` file or touches an existing one, the file should start with the copyright and license header and have an empty line after it, as shown in the example below:
+
+```powershell
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+
+```
+
+Do not place blank lines, comments, or code before this header.
+
+## Requirements
+
+- Add the copyright header when creating a new `.ps1` or `.psm1` file.
+- Preserve the header when editing an existing `.ps1` or `.psm1` file.
+- If an existing `.ps1` or `.psm1` file is missing the header, only modify that file to add the header if a change touches that file. Do not make a change to add the header if the file is not being modified.