Add example multi-output regression

[isaac-chung]

Resolves issue #1057, regarding adding an example for multi-output (multi-label) regression.

[mfeurer]

This example looks good to me, thanks a lot for your contribution.

What do you think about adding another cell which shows the configuration space to demonstrate that it is reduced (i.e. no SVM)?

[isaac-chung]

Thanks @mfeurer .

And sure. Would it be simply a call to print(automl.get_configuration_space(X_train, y_train))?

[mfeurer]

Yes, exactly, thanks a lot. Will merge once the checks are done.

[codecov]

Codecov Report

Merging #1136 (883c92d) into development (0982410) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           development    #1136      +/-   ##
===============================================
- Coverage        85.83%   85.81%   -0.02%     
===============================================
  Files              137      137              
  Lines            10625    10625              
===============================================
- Hits              9120     9118       -2     
- Misses            1505     1507       +2     

Impacted Files	Coverage Δ
...ine/components/feature_preprocessing/kernel_pca.py	94.73% <0.00%> (-1.76%)	⬇️
..._preprocessing/select_percentile_classification.py	87.93% <0.00%> (-1.73%)	⬇️
autosklearn/ensemble_builder.py	76.65% <0.00%> (-0.41%)	⬇️
...ine/components/classification/gradient_boosting.py	92.17% <0.00%> (+0.86%)	⬆️
...ature_preprocessing/select_rates_classification.py	87.32% <0.00%> (+1.40%)	⬆️

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