Give learners "tags" like in mlr3pipelines

[sebffischer]

I think it would be a good addition to tag learners according to the category to which they belong. E.g. in mlr3extralearners we have many different implementations of very similar algorithms.

Tags I am thinking about are:

• Bayesian
• Boosting
• Neural Network
• Decision Tree
• Ensemble Method
• Random Forest

...

This could also be used in the learner help pages to suggest similar learners in the "seealso" section

[mllg]

Where are these tags stored? In the learner or the dictionary? seealso doesn't work across packages.

[sebffischer]

In mlr3pipelines they are stored in the PipeOp. Ok then maybe not in seealso but somewhere else in the description