Change default final_model in StackingEnsemble

[alex-hse-repository]

🚀 Feature Request

Experiments show that linear regression with positive coefficients shows better results comparing with no restrictions to the coefficients. So it is better to change the default final_model in StackingEnsemble to LinearRegression(positive=True)

Proposal

Change the default value to LinearRegression(positive=True) in the constructor of StackingEnsemble here:

etna/etna/ensembles/stacking_ensemble.py

Line 93 in 2b8a527

self.final_model = LinearRegression() if final_model is None else final_model

Test cases

No response

Additional context

No response

[looopka]

let me take this issue?

[alex-hse-repository]

@looopka You can take any "Good first issue" you like)

[ostreech1997]

Closed by #1238