chore: Add Andy Stoneberg as Kubeflow maintainer

related slack thread here:
- https://cloud-native.slack.com/archives/C08NY1D0NUQ/p1755185537599619?thread_ts=1755174449.432219&cid=C08NY1D0NUQ

Signed-off-by: Andy Stoneberg <[email protected]>

Author: andyatmiami

project-maintainers.csv

@@ -1575,6 +1575,7 @@ Sandbox,kcp,Andy Anderson,IBM,clubanderson,https://github.com/kcp-dev/kcp/blob/m
 Incubating,Kubeflow,Aldo Culquicondor,Google,alculquicondor,https://github.com/kubeflow/community/blob/master/MAINTAINERS.md
 ,,Amber Graner,Independent,akgraner,
 ,,Andrey Velichkevich,Apple,andreyvelich,
+,,Andy Stoneberg,Red Hat,andyatmiami,
 ,,Animesh Singh,LinkedIn,animeshsingh,
 ,,Ce Gao,TensorChord,gaocegege,
 ,,Chen Sun,Google,chensun,