Leverage XDS v3 protocol when limited by SMI

[draychev]

SMI provides us with a rich set of primitives to configure our service mesh. SMI does not cover the entire set of features Envoy proxy provides. A service mesh operator, who needs functionality which exists in Envoy but is not serviced via SMI would reach a cliff. To provide a way beyond what SMI currently offers we need to provide the ability for an OSM user to switch to xDS v3 protocol directly.

One such example is the use of a new CRD to configure Envoy circuit breaking - example is in our ./experimental folder.

We need to develop the example we have further to provide more of xDS v3 directly configurable via a CRD.

[nojnhuh]

@draychev Are there any more PRs or issues related to this in flight? If so, could you keep linking back to this issue so we can keep track of those?