Update release notes for v1 release

- Mark this as the v1 release, not preparation for it
- Keep breaking change documentation

Signed-off-by: Mathias L. Baumann <mathias.baumann@frequenz.com>

Author: Marenz

RELEASE_NOTES.md

@@ -2,7 +2,7 @@
 
 ## Summary
 
-Major release preparing for v1 with breaking changes to authentication parameters and dependency updates.
+Major v1 release with breaking changes to authentication parameters and dependency updates.
 
 ## Upgrading