Updating Azure.Identity changelog for 1.5.0-beta.4 release (Azure#23880)

* Updating Azure.Identity changelog for 1.5.0-beta.4 release

* remove unused header

* Update sdk/identity/Azure.Identity/CHANGELOG.md

Co-authored-by: Christopher Scott <chriscott@hotmail.com>

Co-authored-by: Christopher Scott <chriscott@hotmail.com>

Author: schaabs

sdk/identity/Azure.Identity/CHANGELOG.md

@@ -1,18 +1,22 @@
 # Release History
 
-## 1.5.0-beta.4 (Unreleased)
+## 1.5.0-beta.4 (2021-09-08)
 
 ### Features Added
 
 - `DefaultAzureCredentialOptions` now has a `InteractiveBrowserClientId` property which allows passing a ClientId value to the InteractiveBrowserCredential` when constructing a `DefaultAzureCredential`.
 - Implement `OnBehalfOfCredential` which enables authentication to Azure Active Directory using an On-Behalf-Of flow.
-
-### Breaking Changes
+- Added support to `ManagedIdentityCredential` for Azure hosts using federated token exchange for managed identity.
 
 ### Bugs Fixed
+- Refactored IMDS discovery to remove socket probing and caching of failures to improve `ManagedIdentityCredential` resiliency. [#23028](https://github.com/Azure/azure-sdk-for-net/issues/23028)
+- Updated `UsernamePasswordCredential` to use cached tokens when available [#23324](https://github.com/Azure/azure-sdk-for-net/issues/23324)
 
 ### Other Changes
 
+- Updated credentials using `MsalConfidentialClient` to include MSAL log output in logs
+- Added additional logging to `AzureCliCredential`, `AzurePowerShellCredential`, `VisualStudioCrednetial`, and `VisualStudioCodeCredential` when IsPIILoggingEnabled` is set to true.
+
 ## 1.5.0-beta.3 (2021-08-10)
 
 ### Acknowledgments