[BUG or INTENDED?] optim.sched vs optim and sched on same level
Reading through https://github.com/NVIDIA/NeMo/blob/main/examples/tts/conf/hifigan/hifigan.yaml, I noticed that hifigan specifies the `optim` and `sched` on the same level, on quick check in other config files the `sched` is a sub parameter of `optim`. Any special reason?

Checking out the docs https://docs.nvidia.com/deeplearning/nemo/user-guide/docs/en/stable/core/core.html?highlight=scheduler#optimization, https://github.com/NVIDIA/NeMo/blob/main/docs/source/core/core.rst#optimization, I notice that it is quite misleading. It is not evident which version is the correct one. 
