Change watchdog log from "NCCL" to "Process group" (#118121)
This PR changes the watchdog log.
In order to avoid confusion that NCCL creates a watchdog thread and reports the error log, it is better to change "NCCL" to "Process group" to better indicate the source of the log.
@wconstab
Pull Request resolved: https://github.com/pytorch/pytorch/pull/118121
Approved by: https://github.com/kwen2501, https://github.com/wconstab
