Checkpointing fixes

[ashors1]

What does this PR do ?

• converts relative paths to absolute paths before checkpoint saving/loading. This works around the problem of ray workers having different relative dirs
• adds LR scheduler state to the checkpoint

Changelog

• Please update the CHANGELOG.md under next version with high level changes in this PR.

Usage

• You can potentially add a usage example below

# Add a code snippet demonstrating how to use this 

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• Make sure you read and followed Contributor guidelines
• Did you write any new necessary tests?
• Did you add or update any necessary documentation? Make sure to also update the NeMo Framework User Guide which contains the tutorials

Checklist when contributing

• TBD

Additional Information

• Related to # (issue)