The follow error shows up in the wasm cacher logs after upgrading a 2.0 control plane to 2.1.

2021-10-20T18:15:11.743601Z	error	klog	github.com/maistra/xns-informer/pkg/informers/informer.go:164: Failed to watch *v1.ServiceMeshExtension: failed to list *v1.ServiceMeshExtension: servicemeshextensions.maistra.io is forbidden: User "system:serviceaccount:istio-system:wasm-cacher-basic" cannot list resource "servicemeshextensions" in API group "maistra.io" in the namespace "bookinfo"

Steps to reproduce:

1. Create a control plane with smcp.spec.version=v2.0.  Do not enable the tech preview service mesh extensions feature.
2. Modify smcp.spec.version from v2.0 to v2.1
3. Error should appear in the wasm cacher logs
4. Error should disappear once the members have reconciled, following the control plane reconciliation

This is a transient problem, which is caused by service mesh extensions being disabled in 2.0, but enabled by default in 2.1.  Because of this, the existing members do not contain the necessary RoleBinding to allow the cacher to access ServiceMeshExtension resources.  Once the members have been reconciled, and the RoleBinding resources exist, the error is corrected.