feat: Add XSD Code Generator for ISO 20022 message classes

- Implemented PowerShell script (Generate-Classes.ps1) for generating C# classes from XSD files.
- Developed main application (Program.cs) to handle class generation using xsd.exe.
- Created project file (XsdCodeGenerator.csproj) for .NET 8.0 SDK compatibility.
- Added comprehensive documentation for usage, features, and troubleshooting.
- Enhanced generated classes with auto-generated headers, XML documentation, and attributes.
- Included error handling and smart path discovery for xsd.exe.

Author: cleilson pereira