Fix export of configuration parameters to Weights and Biases
@ericharper @titu1994 can you trigger the Nemo_CICD_Test, cicd-test-container-setup, and gpu-test actions?
# What does this PR do ?

This PR corrects an error in ModelPT.py that only partially converts the _hparams_initial from an OmegaConf object to a dictionary before exporting to the various loggers. 

This was particularly an issue with search functionality based on metadata in Weights and Biases due to the cfg object being a string representation of the OmegaConf object.

**Collection**: Core

# Changelog 
- Adds an additional check and conversion of the OmegaConf self._cfg to ensure that Logger.log_hyperparameters from Pytorch Lightning is guaranteed to find a JSON compatible structure at L1650 of core/classes/ModelPT.py

## Reference Images

### Prior to fix

cfg is recorded as a str(OmegaConf.DictConfig) in Weights and Biases 

![Screenshot 2024-10-22 at 11 21 02](https://github.com/user-attachments/assets/740ae152-8f53-4789-aea5-4884361c83e4)


### After fix

cfg is correctly searchable in Weights and Biases

![Screenshot 2024-10-22 at 11 21 17](https://github.com/user-attachments/assets/505d5871-d4cf-4e58-9009-f1198a697374)


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# Additional Information
* Related to # (issue) LLM-5007
