Get more informative timeout variable names or clarify them in the comments

Could the variable `timeout` in line 6318 of the [scheduler](https://github.com/dask/distributed/blob/main/distributed/scheduler.py) have a more sensible name?

I have no idea how to configure that parameter in the yaml configuration file. I have resorted to manually set that value to 600 seconds in my own copy of the code, because I have not been able to configure it. I have tried:

- jobqueue.slurm.connect-timeout
- jobqueue.slurm.tcp-timeout
- jobqueue.slurm.no-workers-timeout
- jobqueue.slurm.death-timeout
- jobqueue.slurm.timeout

None of those correspond to that timeout variable.

Thanks