Sync Istio 1.28.0 with registry (#1723)

Author: kolodziejczak

external-images.yaml

@@ -1,7 +1,7 @@
 images:
-  - source: "istio/pilot:1.27.1-distroless"
-  - source: "istio/proxyv2:1.27.1-distroless"
-  - source: "istio/install-cni:1.27.1-distroless"
-  - source: "istio/ztunnel:1.27.1-distroless"
+  - source: "istio/pilot:1.28.0-distroless"
+  - source: "istio/proxyv2:1.28.0-distroless"
+  - source: "istio/install-cni:1.28.0-distroless"
+  - source: "istio/ztunnel:1.28.0-distroless"
   - source: "kennethreitz/httpbin:latest"
     amd64Only: true