Support Microsoft feature flag schema

[amerjusupovic]

The .NET Microsoft.FeatureManagement library began supporting the Microsoft feature flag schema in the version 3.2.0 release. The provider should follow this pattern and stop emitting the old .NET schema in favor of the Microsoft schema.

The next v8 release of the provider will consequently not work with older versions of the Microsoft.FeatureManagement library that still use the old schema. There should be a warning log on refresh of the provider that will inform the user that their package versions are conflicting if 8.0.0-preview.3 or later of the provider is used with any version of Microsoft.FeatureManagement that was released before 3.2.0.

[amerjusupovic]

The provider should now support both schemas and will output them into configuration depending on what properties are used. If a feature flag does not contain any of the new properties added in v8 preview (variants, allocation, telemetry) then it will be processed using the old schema. Otherwise, it will use the new Microsoft schema linked above.