Update changelog for v0.5.0 release and set version to 0.5.0 in project files

Author: nadeem-cs

CHANGELOG.md

@@ -1,4 +1,10 @@
 # Changelog
+## [v0.5.0](https://github.com/contentstack/contentstack-management-dotnet/tree/v0.5.0)
+ - Feat
+   - **Variant Group Management**: Added comprehensive support for variant group operations
+     - Added `VariantGroup` model class with Find, LinkContentTypes and UnlinkContentTypes methods
+     - Comprehensive unit test coverage with 33+ tests covering all functionality and edge cases
+
 ## [v0.4.0](https://github.com/contentstack/contentstack-management-dotnet/tree/v0.4.0)
  - Feat
    - **MFA Support**: Added Multi-Factor Authentication (MFA) support for login operations

Contentstack.Management.Core/ContentstackClient.cs

@@ -35,7 +35,7 @@ public class ContentstackClient : IContentstackClient
         private HttpClient _httpClient;
         private bool _disposed = false;
 
-        private string Version => "0.4.0";
+        private string Version => "0.5.0";
         private string xUserAgent => $"contentstack-management-dotnet/{Version}";
 
         // OAuth token storage

Directory.Build.props

@@ -1,5 +1,5 @@
 <Project>
   <PropertyGroup>
-    <Version>0.4.0</Version>
+    <Version>0.5.0</Version>
   </PropertyGroup>
 </Project>