add chat sft dataset to support agent tool calling

[chenrui17]

What does this PR do ?

Add a one line overview of what this PR aims to accomplish.

Collection: [Note which collection this PR will affect]

Changelog

• Add specific line by line info of high level changes in this PR.

Usage

• You can potentially add a usage example below

# Add a code snippet demonstrating how to use this 

GitHub Actions CI

The Jenkins CI system has been replaced by GitHub Actions self-hosted runners.

The GitHub Actions CI will run automatically when the "Run CICD" label is added to the PR.
To re-run CI remove and add the label again.
To run CI on an untrusted fork, a NeMo user with write access must first click "Approve and run".

Before your PR is "Ready for review"

Pre checks:

• Make sure you read and followed Contributor guidelines
• 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:

• 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 contains specific people who can review PRs to various areas.

Additional Information

• Related to # (issue)

[cuichenx]

Thanks for the contribution! I would suggest updating the docstring of _mask_targets to explain this update (something like, "If there is more than 1 masked role, mask_role is a comma-separated string of the roles")

[github-actions]

beep boop 🤖: 🙏 The following files have warnings. In case you are familiar with these, please try helping us to improve the code base.

---

Your code was analyzed with PyLint. The following annotations have been identified:

************* Module nemo.collections.nlp.data.language_modeling.megatron.gpt_sft_chat_dataset
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:113:0: C0301: Line too long (165/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:116:0: C0301: Line too long (144/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:147:0: C0301: Line too long (132/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:156:0: C0301: Line too long (165/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:177:0: C0301: Line too long (169/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:240:0: C0301: Line too long (124/119) (line-too-long)
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:59:0: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:182:0: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/nlp/data/language_modeling/megatron/gpt_sft_chat_dataset.py:311:0: C0115: Missing class docstring (missing-class-docstring)

-----------------------------------
Your code has been rated at 9.52/10

---

Mitigation guide:

• Add sensible and useful docstrings to functions and methods
• For trivial methods like getter/setters, consider adding # pylint: disable=C0116 inside the function itself
• To disable multiple functions/methods at once, put a # pylint: disable=C0116 before the first and a # pylint: enable=C0116 after the last.

By applying these rules, we reduce the occurance of this message in future.

Thank you for improving NeMo's documentation!

[cuichenx]

LGTM!