Add worker config options to config system

It seems that many of the `dask-worker` CLI flags and `Worker`/`Nanny` kwargs are not configurable via the Dask config system.

In the work we are doing on the Dask Kubernetes Operator it would be really useful for more things to be configurable via environment variables. Setting things like the worker name, listen address and contact address would be particularly useful.

I intend to make a PR to add more of these options to the `distributed.yaml` config.