fix(cilium): Switch to oci chart

Why OCI Registries?

Storing Helm charts in OCI registries alongside container images offers several advantages:

- Signed charts — All charts are signed with cosign for verification
- Simpler setup — No repository configuration needed
- Digest pinning — Reference exact chart versions by SHA for reproducibility
- Unified tooling — Use the same registry infrastructure for images and charts

helmfile.d/cilium.yaml.gotmpl

@@ -3,7 +3,8 @@ bases:
 
 repositories:
 - name: cilium
-  url: 'https://helm.cilium.io'
+  oci: true
+  url: 'quay.io/cilium/charts'
 
 commonLabels:
   tier: system