Consistent L1/L2 names between EvoLinear and EvoTrees

[ParadaCarleton]

In EvoTrees, the L1/L2 regularizations are called gamma and lambda, respectively; would it be better to have consistent names for these between the two packages?

[jeremiedb]

Arguments naming have emerged from different considerations. Notably, EvoTrees got inspired by existing libraries naming practices (XGBoost), while I approached EvoLinear more as a clean slate. The interpretation of the gamma is also different as it can also be interprated as a tree pruning argument. I prefer not to bring changes to these names unless it comes with some material changes to their logic, justifying adpotions of new names. Otherwise, I prefer applying some L1 to API changes and not bring changes only for the sake of naming.