Feature request: add allele counts to final output

[rjcorb]

Purpose/implementation Section

Briefly describe the feature and provide meaningful references

Add ref and alt allele counts from VCF FORMAT/AD field to final output

What input data are required for this feature or analysis?

How do you plan to organise the feature or analysis - will it be a multi-function call or add to existing functions?

Who will complete the feature request (please add a GitHub handle here if relevant)?

@rjcorb