Pull and parse parent devfile from Kubernetes CRD in library

[yangcao77]

Currently devfile library can only parse parent devfile if uri is specified.

This issue is to support Kubernetes CRD defined under parent.
(Question: should be with type DevWorkspaceTemplate or DevWorkspace ??)

Needs to get KubeConfig and creates Kubernetes client, and access the Kubernetes CRD from that client.

The parent devfile should be parsed & override & merge into the flattened devfile.

[maysunfaisal]

Before starting we should check with the devworkspace operator repo and if they have logic in place for this issue already and needs consolidation..

[yangcao77]

Talked with Angel, devworkspace operator now gets plugin from CRD via the same mechanism. They are going to help port over the common functions(get KubeConfig and creates Kubernetes client, and access the Kubernetes CRD from that client) & tests into library