Adjust lr for AdamW from LAMB default
Signed-off-by: Jocelyn Huang <jocelynh@nvidia.com>

# What does this PR do ?

Adjusts default learning rate down to 1e-3 due to change in default optimizer to AdamW from LAMB (see PR #4233)

**Collection**: TTS

# Changelog 
- Changes default learning rate from 1e-1 to 1e-3 for FastPitch and Mixer-TTS models