Add PowerShell module and testing Copilot instructions

[rulasg]

Guidelines for PowerShell modules and tests:

• .github/copilot-instructions.md: Added instructions for PowerShell functions, including the use of the CmdletBinding attribute, param keyword, and Export-ModuleFunction statement.
• .github/copilot-instructions.md: Added guidelines for writing PowerShell test functions, specifying naming conventions, the use of Assert-NotImplemented, and the inclusion of Arrange, Act, and Assert sections.This pull request adds new instructions for writing PowerShell modules and tests to the .github/copilot-instructions.md file. The most important changes include guidelines for structuring PowerShell functions and tests to ensure consistency and readability.