Evaluate if an optional process can prepare Exome-Kit files

[apeltzer]

We should evaluate whether we can automatically prepare Exome-Kit files for the pipeline if users don't specify explicitly which BED files to use for a certain exome kit. Currently, we only have documentation up that suggests how to achieve that, but this process could potentially be automatically performed, too.

[apeltzer]

Migrated to nf-core#5