Ensure access to MultiQC source files

[pdiakumis]

MultiQC is great and will soon hopefully have more support, but we should not be relying on its JSON exporter to capture all the metrics of interest. Instead, we should ensure we have access to the raw source files with the metrics. We could then even utilise some of MultiQC's Python modules to parse difficult files if needed.

• See ctDNA TSO500 workflow: copy several temp files into final Results cwl-ica#449