Add .NET provider release notes for 7.3.0 (#940)

* add release notes for 7.3.0

* PR comments

releaseNotes/MicrosoftAzureAppConfigurationAspNetCore.md

@@ -1,6 +1,9 @@
 # Microsoft.Azure.AppConfiguration.AspNetCore
 [Source code][source_code] | [Package (NuGet)][package]
 
+## 7.3.0 - July 16th, 2024
+* Updated `Microsoft.Extensions.Configuration.AzureAppConfiguration` reference to `7.3.0`. See the [release notes](./MicrosoftExtensionsConfigurationAzureAppConfiguration.md) for more information on the changes.
+
 ## 7.2.0 - May 2, 2024
 ### Enhancements
 * Added support for .NET 8 as a target framework. [#530](https://github.com/Azure/AppConfiguration-DotnetProvider/issues/530)

releaseNotes/MicrosoftAzureAppConfigurationFunctionsWorker.md

@@ -1,6 +1,9 @@
 # Microsoft.Azure.AppConfiguration.Functions.Worker
 [Source code][source_code] | [Package (NuGet)][package]
 
+## 7.3.0 - July 16th, 2024
+* Updated `Microsoft.Extensions.Configuration.AzureAppConfiguration` reference to `7.3.0`. See the [release notes](./MicrosoftExtensionsConfigurationAzureAppConfiguration.md) for more information on the changes.
+
 ## 7.2.0 - May 2, 2024
 ### Enhancements
 * Added support for .NET 8 as a target framework. [#530](https://github.com/Azure/AppConfiguration-DotnetProvider/issues/530)

releaseNotes/MicrosoftExtensionsConfigurationAzureAppConfiguration.md

@@ -1,6 +1,13 @@
 # Microsoft.Extensions.Configuration.AzureAppConfiguration
 [Source code][source_code] | [Package (NuGet)][package]
 
+## 7.3.0 - July 16th, 2024
+### Enhancements
+* Upgraded the package reference for `Azure.Security.KeyVault.Secrets` to `4.6.0`. [#572](https://github.com/Azure/AppConfiguration-DotnetProvider/pull/572)
+
+### Bug Fixes
+* Loading invalid feature flags should no longer throw an error when `TryRefreshAsync` is invoked or when the `optional` argument is true in the `AddAzureAppConfiguration` method. [#551](https://github.com/Azure/AppConfiguration-DotnetProvider/pull/551)
+
 ## 7.2.0 - May 2, 2024
 ### Enhancements
 * Added support for .NET 8 as a target framework. [#530](https://github.com/Azure/AppConfiguration-DotnetProvider/issues/530)