feat: re-enable `require-image-signature` policy

General MR

Summary

Re-enables the kyverno policy require-image-signature after some enhancements were made to the kyverno-policies helm chart.

Issues

relates #1821 (closed) relates big-bang/product/packages/kyverno-policies#9 (closed) closes #1777 (closed)

chart/templates/kyverno-policies/values.yaml

@@ -233,7 +233,7 @@ policies:
 
   # Kyverno Beta feature - https://kyverno.io/docs/writing-policies/verify-images/
   require-image-signature:
-    enabled: false
+    enabled: true
     validationFailureAction: audit
 
   require-istio-on-namespaces: