roc_auc_weighted metric addition (#827)

* Pending changes exported from your codespace

* Update flaml/automl.py

Co-authored-by: Chi Wang <wang.chi@microsoft.com>

* Update flaml/automl.py

Co-authored-by: Chi Wang <wang.chi@microsoft.com>

* Update flaml/ml.py

Co-authored-by: Chi Wang <wang.chi@microsoft.com>

* Update flaml/ml.py

Co-authored-by: Chi Wang <wang.chi@microsoft.com>

* Update website/docs/Examples/Integrate - Scikit-learn Pipeline.md

Co-authored-by: Chi Wang <wang.chi@microsoft.com>

* added documentation for new metric

* Update flaml/ml.py

Co-authored-by: Chi Wang <wang.chi@microsoft.com>

* minor notebook changes

* Update Integrate - Scikit-learn Pipeline.md

* Update notebook/automl_classification.ipynb

Co-authored-by: Chi Wang <wang.chi@microsoft.com>

* Update integrate_azureml.ipynb

Co-authored-by: Chi Wang <wang.chi@microsoft.com>