add init group during exp manager
# What does this PR do ?

Add a one line overview of what this PR aims to accomplish.

Fixes https://github.com/NVIDIA/NeMo/issues/7460. Exp manager now initializes distributed groups to force a barrier.

# Changelog 
- Add specific line by line info of high level changes in this PR.


  
**PR Type**:
- [ ] New Feature
- [x] Bugfix
- [ ] Documentation

# Additional Information
* Related to # (issue)
#7460 
