Add DSC v3 module template with build and configuration scripts

[Gijsreyn]

Pull Request

Pull Request (PR) description

Adds a new DscV3Module Plaster template for scaffolding DSC v3 PowerShell modules with class-based resources.

Added

• New DscV3Module template with complete project scaffolding
• DscV3Manifest.build.ps1 build task for generating DSC v3 manifests
• Template includes: build configuration, VS Code settings, sample FileContent resource, and Pester tests

Task list

• The PR represents a single logical change.
• Added an entry under the Unreleased section of in the CHANGELOG.md.
• Local clean build passes without issue or fail tests.
• Documentation added/updated in README.md.
• Comment-based help added/updated.
• Localization strings added/updated in all localization files as appropriate.
• Unit tests added/updated.
• Integration tests added/updated (where possible).
• New/changed code adheres to DSC Community Style Guidelines.

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