Added Neptune logger support
Hi, thanks for the additional support for Neptune. Due to the ever growing dependency list for NeMo, we will make Neptune an optional dependency only. Please follow the suggestions above  Oh also, could you follow DCOBot comments to sign your commits since that is a NeMo contribution requirement.  > Oh also, could you follow DCOBot comments to sign your commits since that is a NeMo contribution requirement.

I have amended the commits to include Sign off. > Hi, thanks for the additional support for Neptune. Due to the ever growing dependency list for NeMo, we will make Neptune an optional dependency only. Please follow the suggestions above

Got that, have made the changes to remove dependency from the requirements files.
# What does this PR do ?

Adds Neptune logging support to NeMo which is already exposed by the PTL trainer.

**Collection**: [Note which collection this PR will affect]
Affects the core/experiment manager collection

# Changelog 
- In experiment manager, consumed NeptuneLogger parameters from the OmegaConf
- Added tests for NeptuneLogger
- Added documentation for NeptuneLogger configuration

# Usage
* Can be directly used by configuring the mentioned keys in the docs under exp_manager similar to how WandB params are specified.

```python
# Add a code snippet demonstrating how to use this 
```

# Jenkins CI
To run Jenkins, a NeMo User with write access must comment `jenkins` on the PR.

# 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?
- [x] 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.
@ericharper 

# Additional Information
* Related to # (issue)
