Support Falcon Variants (7B/40B/180B) in Mcore NeMo
# What does this PR do ?

Conversion script for HuggingFace Falcon checkpoint (1b-rw/7b-rw/7b/40b/180b) to NeMo format, as well as NeMo to HuggingFace format.
Support Falcon parallel attention and new decoder architecture by adding falcon_decoder_layer and falcon_spec,
these will make use of mcore's latest spec system. 

Limitation: although the conversion script works for 1b-rw/7b-rw, Alibi is currently not supported in mcore GPT, so expect suboptimal generation results from these two models that use Alibi specifically. This limitation will NOT affect other 7b/40b/180b Falcon variants. 

**Collection**: [Note which collection this PR will affect]

# Changelog 
- add bi-directional HF <-> NeMo conversion script
- Falcon architecture implemented using mcore spec system and mcore layers.

# Usage
* See docstring in the conversion script on how to use. 

# 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)
- [x] Did you write any new necessary tests?
- [ ] Did you add or update any necessary documentation?
- [ ] 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
- [ ] 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.

# Additional Information
* Related to # (issue)
