Optimizing distributed Adam when running with one work queue
# What does this PR do ?

When running GPT with `CUDA_DEVICE_MAX_CONNECTIONS=1`, @erhoo82 observed poor overlapping between the backward compute and the gradient reduce-scatters in the distributed Adam optimizer. This PR integrates performance optimizations from https://github.com/NVIDIA/apex/pull/1551.

I haven't fully tested, but this also seems to fix a hang that occurs when running with 32+ Selene nodes.

**Collection**: NLP

# Changelog 

- Manually configure dist Adam for GPT, T5, and BERT so each Transformer layer occupies one effective param bucket.
- Make sure dist Adam reduce-scatters are synchronized before all-reducing embedding gradients.

# Usage

Set the optimizer to `distributed_fused_adam` in the config file: https://github.com/NVIDIA/NeMo/blob/f1c8714f2fe0bc18a338fb02f0e608144981b291/examples/nlp/language_modeling/conf/megatron_gpt_config.yaml#L192

# Before your PR is "Ready for review"
**Pre checks**:
- [x] Make sure you read and followed [Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md)
- [ ] Did you write any new necessary tests?
- [ ] Did you add or update any necessary documentation?
- [x] Does the PR affect components that are optional to install? (Ex: Numba, Pynini, Apex etc)
  - [ ] Reviewer: Does the PR have correct import guards for all optional libraries?
  
**PR Type**:
- [x] New Feature
- [x] Bugfix
- [ ] Documentation

If you haven't finished some of the above items you can still open "Draft" PR.


## Who can review?

Anyone in the community is free to review the PR once the checks have passed. 
[Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md) contains specific people who can review PRs to various areas.

Pinging @erhoo82 and @markelsanz14.

# Additional Information
* Depends on https://github.com/NVIDIA/apex/pull/1551