add checkpoint_max_to_keep to train_loop

[FirdowsRahaman]

Description

📝 Summary of the change.

• Sometimes we need more checkpoints to evaluate the trained model. If the user can define that on command line it'll help them to test and get a better model.
• No dependencies that are required for this change.

Type of change

• Other (Add checkpoint_max_to_keep argument to train_loop function)

Tests

📝 Please describe the tests that you ran to verify your changes.

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Test Configuration:

Checklist

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• My code follows the coding guidelines.
• I have performed a self code review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
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• I have added tests that prove my fix is effective or that my feature works.

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