Add custom callable metric

[mike0sv]

import pandas as pd

from evidently.base_metric import InputData
from evidently.metrics.custom_metric import CustomCallableMetric
from evidently.report import Report


def func(data: InputData):
    return .5


def main():
    report = Report(metrics=[CustomCallableMetric(func=func, title="kek")])

    data = pd.DataFrame({"a": [1, 2, 3]})
    report.run(reference_data=data, current_data=data)

    report.save_html("CustomCallableMetric.html")
    report.to_snapshot().save("CustomCallableMetric.json")


if __name__ == '__main__':
    main()