docs(dynamic-links): add not on auth use case to Dynamic Link deprecation notice (#7773)

* Update Dynamic Link Warning

Firebase Dynamic Links is deprecated for primary use cases of store/web routing and regular/deferred deep-linking.

It is NOT deprecated for the usage of Firebase Authentication.  It is, and will continue to be, required as a dependency for the handling of password reset and password-less sign in links beyond the August 25, 2025 deadline.

* Update docs/dynamic-links/usage/index.md

---------

Co-authored-by: Mike Hardy <[email protected]>

Author: skam22

docs/dynamic-links/usage/index.md

@@ -7,7 +7,7 @@ previous: /database/presence-detection
 ---
 
 > [!WARNING]
-> Deprecated: Firebase Dynamic Links is deprecated and should not be adopted in projects that don't already use it. The service will shut down on August 25, 2025. See the [Dynamic Links Deprecation FAQ](https://firebase.google.com/support/dynamic-links-faq) for more information.
+> Deprecated: Firebase Dynamic Links is deprecated and should not be adopted in projects that don't already use it. Functionality for the primary use cases of store/web routing and deferred/regular deep-linking will shut down on August 25, 2025. Firebase Authentication currently uses Firebase Dynamic Links to customize Authentication links, but the Firebase team will provide an update to ensure that this functionality continues working after the Firebase Dynamic Links service is shut down. See the [Dynamic Links Deprecation FAQ](https://firebase.google.com/support/dynamic-links-faq) for more information.
 
 # Installation