[Core] Use language independent worker initiators

[chenk008]

Describe your feature request

Currently, ray supports Python/Java/C++ workers, raylet will fork one language worker on demand. Now runtime env can works with python worker, but don't support Java/C++ workers.

How about add an language independent worker initiators? I think we can use setup_worker.py as the initiator , and the initiator will setup worker enviroment (e.g. create a container).

When we want to create k8s native worker Pod , the initiator can create Pod.

The new workflow looks like:

[jovany-wang]

It makes sense to me.

[raulchen]

Sounds good. And we should move the language-specific code from the worker pool to the initiator. cc @SongGuyang