labels kwarg for default_pod / K8sNativeManager / addprocs_pod

[kolia]

Right now labels can be set by passing in a configure closure, which is clunky.

Users should be able to pass in labels as kwargs, the same way as memory, cpu, etc.

Maybe even set a label by default, maybe name: <driver-pod-id>?

[omus]

Maybe even set a label by default, maybe name: <driver-pod-id>?

Some default labels would be nice. We should probably have a label that is used for the manager and worker pods (e.g. cluster: <driver-pod-id>) and a label just for the worker pods (e.g. worker: <driver-pod-id>).

The later already has a PR: #38

[omus]

Workers now automatically have a worker-id label which is the same as there worker ID (myid) as of #48