Add Model Ensembling Tutorial (#640)

* add model ensembling tutorial

* update ensembling notebook

* refractor codes

* Revamped tutorial to include simple borda count

* Restructured model ensembling tutorial

* Update tutorial result representation

* Update tutorial

* Update tutorial

* Update model ensembling tutorial based on feedback

* Update linear regression/random forest inference data set

* WIP Initial experimental calculation

* preliminary calculation of experimental comparison

* Update recall@K and precision@K evaluation

* Add borda count, enhanced wmf to comparison

* Revised model ensembling tutorial

* Fix bug

* Revised markdown and description of tutorial

* Enhance tutorial content

* Simplify introduction

* Enhance tutorial

* Update tutorial

* Updated model ensembling tutorial

* Optimize inference code

* Optimize inference code

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Co-authored-by: tqtg <[email protected]>