Better documentation of required open ports

When trying to deploy dask in a firewalled environment it is important to know the full set of ports that need to be accessible and from where they will be accessed (i.e. source/target/port for all connections between client, scheduler and workers).

Right now I don't think it's very visible in the docs that workers also listen on (random) ports and what the tooling is to fix the ports (and also who connects to these ports -- the scheduler, other workers, the client). So I think it would be useful to have some docs around this specifically geared towards IT admins setting up FW rules. An example of docs like this is:

https://kubernetes.io/docs/reference/ports-and-protocols/

- Enumerate which ports are used in Client <-> Scheduler <-> Worker communications
- Some information around best practices around worker port system (currently only documented in docstrings)
- Currently need to set a flag manually to limit the ports used