Add interface for making amax reduction optional for FP8
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

# What does this PR do ?

Adds interface in NeMo to use Transformer Engine's optional amax reduction feature. Previously, TE would always reduce amaxes by default during fp8 training (across the `fp8_group` specified in `fp8_autocast` API).