Add support for [SecureString] in PowerShell adapter

[Gijsreyn]

PR Summary

This pull request adds support for [SecureString] in class-based DSC resources. Small remediation fix if a user uses the fully qualified property name on [PSCredential].

PR Context

Fix #1207.

[Copilot]

Pull Request Overview

This pull request adds support for [SecureString] type properties in PowerShell class-based DSC resources and fixes handling of fully qualified PSCredential property types.

• Adds conversion logic to handle [SecureString] properties by converting plain text values to secure strings
• Updates PSCredential type checking to use wildcard matching for fully qualified type names
• Adds test coverage for SecureString property handling

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
adapters/powershell/psDscAdapter/psDscAdapter.psm1	Implements SecureString conversion logic and updates PSCredential type matching to handle fully qualified names
adapters/powershell/Tests/powershellgroup.resource.tests.ps1	Adds test case to verify SecureString property processing
adapters/powershell/Tests/TestClassResource/0.0.1/TestClassResource.psm1	Adds SecureStringProp property to test resource for validation

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[Copilot]

The $validateProperty variable is being assigned twice - once at line 427 and again at line 429 inside the if block. This results in a redundant Where-Object query when the value is a PSCustomObject. Consider removing the duplicate assignment at line 429 since line 427 already retrieves the same value.

Suggested change

$validateProperty = $cachedDscResourceInfo.Properties | Where-Object -Property Name -EQ $_.Name

[Copilot]

The condition checks for non-empty string values, but doesn't verify that $_.Value is actually a string type. If $_.Value is a different type (e.g., an integer or boolean), ConvertTo-SecureString -AsPlainText could fail or produce unexpected results. Consider adding a type check to ensure $_.Value -is [string] before attempting the conversion.

Suggested change

	if ($validateProperty -and $validateProperty.PropertyType -like '*SecureString' -and -not [string]::IsNullOrEmpty($_.Value)) {
	if ($validateProperty -and $validateProperty.PropertyType -like '*SecureString' -and $_.Value -is [string] -and -not [string]::IsNullOrEmpty($_.Value)) {