Release note for .NET FM 4.3.0 (#1095)

* add release note for .net fm 4.3.0

* Fix link reference in release notes for 4.3.0

Author: zhiyuanliang-ms

releaseNotes/Microsoft.Featuremanagement.AspNetCore.md

@@ -2,7 +2,13 @@
 
 [Source code][source_code] | [Package (NuGet)][package] | [Samples][samples] | [Product documentation][docs]
 
-## 4.2.1 - July 9, 2025
+## 4.3.0 - August 27, 2025
+
+* Updated `Microsoft.FeatureManagement` reference to `4.3.0`. See the [release notes](./Microsoft.Featuremanagement.md) for more information on the changes.
+
+## 4.2.1 - July 9, 2025 (Delisted)
+
+This release has been delisted due to the enhancement below resulting in an unintended breaking change. For more information, please go to [#550](https://github.com/microsoft/FeatureManagement-Dotnet/issues/550).
 
 * Updated `Microsoft.FeatureManagement` reference to `4.2.1`. See the [release notes](./Microsoft.Featuremanagement.md) for more information on the changes.
 

releaseNotes/Microsoft.Featuremanagement.Telemetry.ApplicationInsights.md

@@ -2,7 +2,13 @@
 
 [Source code][source_code] | [Package (NuGet)][package] | [Samples][samples] | [Product documentation][docs]
 
-## 4.2.1 - July 9, 2025
+## 4.3.0 - August 27, 2025
+
+* Updated `Microsoft.FeatureManagement` reference to `4.3.0`. See the [release notes](./Microsoft.Featuremanagement.md) for more information on the changes.
+
+## 4.2.1 - July 9, 2025 (Delisted)
+
+This release has been delisted due to the enhancement below resulting in an unintended breaking change. For more information, please go to [#550](https://github.com/microsoft/FeatureManagement-Dotnet/issues/550).
 
 * Updated `Microsoft.FeatureManagement` reference to `4.2.1`. See the [release notes](./Microsoft.Featuremanagement.md) for more information on the changes.
 

releaseNotes/Microsoft.Featuremanagement.md

@@ -2,6 +2,12 @@
 
 [Source code][source_code] | [Package (NuGet)][package] | [Samples][samples] | [Product documentation][docs]
 
+## 4.3.0 - August 27, 2025
+
+### Enhancements
+
+* Introduced `ConfigurationFeatureDefinitionProviderOptions` which allows to enable the new configuration merging behavior for the built-in `ConfiguationFeatureDefinitionProvider`. When the same feature flag is defined in multiple sources, definitions are merged according to configuration provider registration order, with the last feature flag definition taking precedence in case of conflicts. [#552](https://github.com/microsoft/FeatureManagement-Dotnet/pull/552)
+
 ## 4.2.1 - July 9, 2025 (Delisted)
 
 This release has been delisted due to the enhancement below resulting in an unintended breaking change. For more information, please go to [#550](https://github.com/microsoft/FeatureManagement-Dotnet/issues/550).