Replace deepvariant process with deepvariant subworkflow

[fellen31]

Description of feature

The deepvariant process could be split into 3 parts and made into a workflow. This would better allocate resources, mainly since the last step is single/threaded and takes some time where the rest of the allocated cores go unused.

[jemten]

That would be of interest for the nf-core/raredisease pipeline as well 😄

[fellen31]

Let's see if we can't do it on nf-core instead: nf-core/modules#5793