Generate separate consumer kubeconfig per user/team

[devdattakulkarni]

KubePlus generates a consumer kubeconfig which can be used by users to create application instances in a self-service manner. Currently, only one consumer kubeconfig is generated by KubePlus. We should support the creation of separate kubeconfig files for different user/teams. Each team should be able to access only their application instance and no one else's.

One way to achieve this will be to tie the consumer kubeconfig to the Namespace. However, in the current model, an application Namespace is created at runtime.

Note that previously KubePlus supported deploying applications in existing Namespaces. But we went away from that model for simplicity reasons. Let's revisit that model as part of this feature.

We have to add a kubectl plugin to generate consumer kubeconfig
kubectl generate consumer kubeconfig <Namespace>

As part of generating the kubeconfig, we should grant the new SA permissions on *.platformapi.kubeplus APIs.