Add GitHub Actions workflow for building SharpShares

[nickvourd]

• Added a Windows-based GitHub Actions build workflow.
• Builds SharpShares using MSBuild on windows-2022.
• Retargets the project from .NET Framework 4.0 to 4.8 during the CI build to support the GitHub Actions runner.
• Supports manual, scheduled, push, and pull request triggers.
• Uploads the compiled SharpShares.exe, configuration file, and PDB as a workflow artifact.
• The workflow also runs automatically every day at 06:00 UTC.
• The generated artifact is published as: SharpShares-dotnet