Mark kep as implementable

Author: g-gaston

keps/sig-auth/4872-harden-kubelet-cert-validation/kep.yaml

@@ -4,7 +4,7 @@ authors:
   - "@g-gaston"
 owning-sig: sig-auth
 participating-sigs:
-status: provisional
+status: implementable
 creation-date: 2024-09-24
 reviewers:
   - TBD