Integrate new classes into main namespace and remove v1alpha8

Signed-off-by: Mathias L. Baumann <[email protected]>

Author: Marenz

RELEASE_NOTES.md

@@ -8,6 +8,8 @@
 
 <!-- Here goes notes on how to upgrade from previous versions, including deprecations and what they should be replaced with -->
 
+- The `v1alpha8` namespace has been removed. This is a breaking change if you were importing directly from `frequenz.client.common.v1alpha8`. The classes have been integrated into the main `frequenz.client.common` namespace, so you might need to update your imports.
+
 ## New Features
 
 <!-- Here goes the main new features and examples or instructions on how to use them -->