Added info about the breaking change concerning the retry policy

Author: wcabus

src/content/docs/accesstokenmanagement/upgrading/atm-v3-to-v4.md

@@ -46,6 +46,11 @@ Instead of relying on implicit behaviors or inheritance, V4 introduces clearly d
 
 The `AccessTokenHandler` has been restructured to use composition rather than inheritance, simplifying the customization of token handling and increasing testability.
 
+As part of these changes, the retry logic that was part of the `AccessTokenHandler`'s functionality in V3 has moved to
+a resiliency policy. If you're not using `AddClientCredentialsHttpClient` to configure an HTTP client, and you depend on the 
+retry policy to be there, you should use `AddDefaultAccessTokenResiliency` to add our implementation or provide your own retry policy.
+See [Service Workers](/accesstokenmanagement/workers.mdx) for more details. 
+
 If you wish to implement a custom access token handling process, for example to implement token exchange, you can now [implement your own `AccessTokenRequestHandler.ITokenRetriever`](/accesstokenmanagement/advanced/extensibility.md#token-retrieval).
 
 ### Strongly Typed Configuration