Shinwool/upstream from bionemo utils scheduler
# What does this PR do ?

Adds a LR scheduler policy (LinearWarmupHoldDecayPolicy) that has following properties:
- Phase 1: linear warmup from 0 to the optimizer's learning rate
- Phase 2: constant phase
- Phase 3: linear decay to 'min_lr'
- Phase 4: constant phase at 'min_lr'
A visual representation of above is included in code.

**Collection**: N/A

# Changelog 
- Added class for LR scheduler policy (LinearWarmupHoldDecayPolicy)
- Added unit test for above

# Usage

# Before your PR is "Ready for review"
**Pre checks**:
- [v] Make sure you read and followed [Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md)
- [v] Did you write any new necessary tests?
- [v] 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**:
- [v] 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)
