Update rl_dataset.py with apply_chat_template

[ZHUI]

Before submitting

• Lint code. If there are lint issues, please format the code first.

# Install and register `pre-commit` in the project folder
pip install pre-commit && pre-commit install

# Process previous code files separately
pre-commit run --file XXXX.py

• Add test cases into tests folder. If there are codecov issues, please add tests cases first.

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Description

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 48.66%. Comparing base (aad5cbe) to head (a795289).
Report is 4 commits behind head on develop.

Files with missing lines	Patch %	Lines
paddlenlp/datasets/rlhf_datasets/rl_dataset.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop   #10510   +/-   ##
========================================
  Coverage    48.66%   48.66%           
========================================
  Files          768      768           
  Lines       126950   126951    +1     
========================================
+ Hits         61779    61781    +2     
+ Misses       65171    65170    -1     

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