Update status for annotation alpha.istio.io/identity

[nmittler]

From https://github.com/istio/api/pull/1723/files#r516404165.

[ ] Configuration Infrastructure [x] Docs [ ] Installation [ ] Networking [ ] Performance and Scalability [ ] Policies and Telemetry [ ] Security [ ] Test and Release [ ] User Experience

Expected behavior

Steps to reproduce the bug

Version (include the output of istioctl version --remote and kubectl version)

How was Istio installed?

Environment where bug was observed (cloud vendor, OS, etc)

[nmittler]

ping @myidpt

[howardjohn]

removed