feat: add instrument context to inst_processor

[PalanQu]

Add instrument context to inst_processor

Description

Many indicator analysis need to use forward adjust stock price, but this price need to be calculated when load the data, so I need to write inst_processor to pre-calculate the forward adjust stock price like following, I want to read the latest adjfactor from source data, but there is no context in call.

class AdjPriceProcessor(InstProcessor):
    def __call__(self, df: pd.DataFrame, *args, **kwargs):
        # TODO: Read the latest adjfactor from source data
        return df

day_fields = ['$close']
day_names = ['close']
labels = ['Ref($close, -2)/Ref($close, -1) - 1'] # label
label_names = ['LABEL']
def feature_config():
    return {
        'feature_day': (
            day_fields,
            day_names,
        ),
        'label': (labels, label_names)
    }

data_loader = QlibDataLoader(
    config=feature_config(),
    freq={
        'label': 'day',
        'feature_day': 'day',
    },
    inst_processor={
        'feature_day': [AdjPriceProcessor()],
        'label': [],
    }
)

df = data_loader.load(instruments=['SH600519', 'SZ300750'], start_time='2020-01-01', end_time='2021-01-01')

Motivation and Context

How Has This Been Tested?

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• [x ] Pass the test by running: pytest qlib/tests/test_all_pipeline.py under upper directory of qlib.
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Screenshots of Test Results (if appropriate):

1. Pipeline test:
2. Your own tests:

Types of changes

• Fix bugs
• [ x] Add new feature
• Update documentation

[you-n-g]

Thanks for your advice! It looks more reasonable to add this parameter.

In addition, I think the interface should be changed with it
https://github.com/microsoft/qlib/blob/main/qlib/data/inst_processor.py#L8

[ghost]

All CLA requirements met.

[you-n-g]

LGTM! Thanks !