Add additional metrics to MultiQC

[nh13]

Description of feature

See: #42 (comment)

E.g. add metrics produced by GroupReadsByUmi: See: https://github.com/MultiQC/MultiQC/blob/main/docs/modules/fgbio.md

Are there additional QC that we should add? It would be useful to have a table where each row is a sample, and each column is the # of reads after a given step. E.g. raw reads (mapped and grouped), consensus calls (total and mapped), filtered calls (total and mapped).

[SPPearce]

Oh yes, a summary of where the reads are "lost" would be really useful.
Potentially also an on-target proportion as generally it is going to be used with a pulldown.