Add Microsoft.FeatureManagement library to Feature Management section

[zhiyuanliang-ms]

Githup repo: https://github.com/microsoft/FeatureManagement-Dotnet
Nuget: https://www.nuget.org/packages/Microsoft.FeatureManagement/3.3.1
Offical doc: https://learn.microsoft.com/en-us/azure/azure-app-configuration/feature-management-dotnet-reference?pivots=stable-version

Feature management provides a way to develop and expose application functionality based on features. Many applications have special requirements when a new feature is developed such as when the feature should be enabled and under what conditions. This library provides a way to define these relationships, and also integrates into common .NET code patterns to make exposing these features possible.

The latest version of feature management offers the variant feature flag and full functionality to support experimentation. This library is evolving from feature flag toggle to experimentation solution.

I believe this library would be a valuable addition to the collection. /smile