supports custom proportions for augument

[chakravarthik27]

Checklist:

• I've added Google style docstrings to my code.
• I've used pydantic for typing when/where necessary.
• I have linted my code
• I have added tests to cover my changes.

[chakravarthik27]

Now, the user can pass Dict or List for custom_proportions while doing augmentation in the harness.

I've included for you the example with the Dict variable. In case, augmentation takes place on selected test names as well as it's values in the range of 0 to 1.

custom_props = {'add_typo': 0.8, 'american_to_british': 0.1}

harness.augment(input_path='../nlptest/data/conll/sample.conll', output_path='./augmentated.conll', 
                custom_proportions=custom_props,
                inplace=True)

I've included for you the example with the List variable. In case only, augmentation takes place on selected test names.

custom_props = ['add_typo', 'american_to_british'] 

harness.augment(input_path='../nlptest/data/conll/sample.conll', output_path='./augmentated.conll', 
                custom_proportions=custom_props,
                inplace=True)