Allow missing/NA-filled columns for sdrf2openms conversion

[jpfeuffer]

In quantms, for simple experiments, I would like to allow using SDRF only to specify the experimental design (incl. channels), not mass spec. related settings (and use nextflow parameters to specify the rest). This is mainly because it is much easier to quickly set enzyme, modifications, tolerance etc. in the nextflow WebUI instead of editing a tsv file with ontology names etc.

For this, the first step would be to allow those three columns to be missing or the entries being "Not Available" in the "sdrf to openms" conversion tool, because we use the config file that comes out of this to fill the meta information channel in nextflow.

As soon as that works, I could change the create_input_channel module to check for missingness in the openms.tsv and use the nextflow params as a fallback.

As discussed with @ypriverol