new module: deseq2/differential

[pinin4fjords]

See https://nfcore.slack.com/archives/CE8SSJV3N/p1664996414210659?thread_ts=1661174347.177469&cid=CE8SSJV3N

Wrapper module for differential analysis with DESeq. I have my own version, and @ggabernet flagged her existing pipeline at https://github.com/qbic-pipelines/rnadeseq.

Suggest keeping differential analysis distinct from plotting, to allow reuse of the latter and facilitate software dependency management per process.