Support RayOnSpark for k8s and add docs (#2836)
Support RayOnSpark for k8s and add docs (#2836)

* support ray on k8s

* add to init orca context

* style

* minor

* minor

* ut
yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL,intel-analytics/BigDL