Adding learner from package sparsediscrim

[AnnaNzrv]

Adding three new classification learners from the package sparsediscrim, that are also used by tidymodels for linear discriminant analysis:

• Diagonal Linear Discriminant Analysis classif learner (dlda)
• Minimum Distance Empirical Bayesian classif learner (mdeb)
• Shrinkage-based Diagonal Linear Discriminant Analysis classif learner (sdlda)

Thank you for contributing a learner to the mlr3 ecosystem.
Please make sure that:

• [X ] The added learner(s) are sufficiently tested
• [X ] All the CI tests are passing (including the CodeFactor)
• [X ] You ran devtools::document()
• You updated the NEWS.md field to include the addition of the learner
• [X ] You did not modify anything not related to the new learner
• [X ] You are listed as a contributor in the DESCRIPTION of the R package