[Auto] Add early stopping strategies

[zhreshold]

Now through config, it can control the early stopping of estimators

early_stop_patience : int = -1  # epochs with no improvement after which train is early stopped, negative: disabled
early_stop_min_delta : float = 0.001  # ignore changes less than min_delta for metrics
early_stop_baseline : Union[float, int] = 0.0 # the baseline value for metric, training won't stop if not reaching baseline
early_stop_max_value : Union[float, int] = 1.0  # early stop if reaching max value instantly

[github-actions]

Job PR-1641-33b1d69 is done.
Docs are uploaded to http://gluon-vision-staging.s3-website-us-west-2.amazonaws.com/PR-1641/33b1d69/index.html