List and descriptions of new features.

A list of large features we should call out in release notes (that may not be covered by other issues) - will try to create tasks for each:

• -New operator for Istio, with Istio CRD replacing ServiceMeshControlPlane
• -Istioctl
• Multi-cluster: Multi-primary, primary-remote, external control planes
• Multiple control planes replace's OSSM 2's multi-tenant mode
• Canary / RevisionBased updates w/ IstioRevision, IstioRevisionTags
• Minimal container images
• "For a full list of changes in OSSM 3 vs 2, please read... https://docs.openshift.com/service-mesh/3.0.0tp1/migrating/ossm-migrating-read-me-assembly.html