For certain resampling methods, there are default confidence interval methods.
See mlr3::mlr_reflections$default_ci_methods for a selection.
This measure will select the appropriate CI method depending on the class of the
used Resampling.
rr = resample(tsk("sonar"), lrn("classif.featureless"), rsmp("holdout"))
rr$aggregate(msr("ci", "classif.acc"))
# is the same as:rr$aggregate(msr("ci.holdout", "classif.acc"))