Feature request: support specifying dashboard port ranges when launching workers with multi-processing.

[Arsenal591]

When starting dask-worker with nworkers > 1, we can specify a port range for --worker-port like 3000:3026. However, the --dashboard-address does not have a similar functionality. Supporting specifying a dashboard address for each worker process would be very helpful in some circumstances.

[jacobtomlinson]

This sounds great! I expect this would be a good first issue for someone as you can look at how the implementation for --worker-port is done and replicate that for --dashboard-address.