Read interval files with multiple columns and annotate a VariantDataset

A lot of annotations are in interval format. For the same interval it is common to have multiple information. For example: chr1:1000-10000 34 ABC 3000 1 2. Where the different values are different information related to that interval.
Now it is possible to read this file as keytable using import_keytable as described here: However is not possible to annotate a VariantDataset using a keytable with an interval key.
therefore it will be good to have a function that allows that, maybe it can simply be a generalization of annotate_variants_keytable to handle intervals.