Allow disabling TLS for workers and schedulers

[orf]

Using TLS between workers and schedulers is appropriate in some situations, but in others it is not required. It also adds a non-trivial overhead and another entire failure mode to a Dask cluster.

Take for example a Dask cluster deployed to Kubernetes within AWS. Within the cluster VPC there isn't a strong need to enable TLS as the security boundary is the cluster. If someone is inside and able to intercept traffic then they are already so past the airtight hatchway that it's not important.

Currently you can't disable TLS. It would be handy to have an option to do so.

[ArieLevs]

We are having an issue with using dask gateway from jupyter notebooks, getting error:

after 10 s: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: self signed certificate (_ssl.c:997)

is it reasonable to add a skip cert verification on self signed certs? or maybe there is an exiting solution with skipping verification? @consideRatio @chenshap

[liefengzheng]

I have the same issue when using dask gateway from jupyter notebooks. There have any ways to disable TLS between workers and schedule