Question about dask operator logic

Wanted to ask a few questions about [this PR](https://github.com/dask/dask-kubernetes/pull/661) that was changing the Dask Kubernetes settings / configuration.

**Firstly,** I may be confused about the `async` addition for `_is_service_available` and what that is doing. I see that it is used in two functions (`get_external_address_for_scheduler_service` and `get_internal_address_for_scheduler_service`) but both of these functions were `async` already. So if used from an async context, I would assume that they would already be non-blocking. Especially since `_is_service_available` is called with `await` I am confused what this modification does. I am not a heavy python async user so please explain like I am 5 years old.

**Secondly,** a friend I have had some concerns about `periodSeconds` being set to `1` , specifically he was under the impression that `timeoutSeconds=300` would cause K8 to create 300 concurrent requests if the health point in question is not responding. I am also relatively new to the liveness probe behavior, is it your understanding that these a probe request will only be created after a probe fails, or that probes may be concurrent?

cc: @jacobtomlinson