v0.6.0-rc.4

Sync manifest v0.6 branch (#220)

* Copy istio to its own package (#205)

* move istio to its own package

* put back gcp/istio*

* make ClusterRbacConfig configurable (#209)

* remove istio from gcp (#212)

* update jupyter web app image (#214)

* Update OWNERS (#215)

* add metadata OWNERS (#218)