Add min boot param

[zmudge3]

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This PR adds a new parameter, dada_min_boot, that corresponds exactly with minBoot in DADA2's assignTaxonomy method. This parameter specifies a minimum bootstrap confidence (out of 100 trials) needed in order to assign a taxonomic level. This can be helpful in order to filter out assignments for ASVs that are likely too specific. E.g. An ASV was assigned to the incorrect species with confidence 55 (0.55), which is quite low, but was assigned to the correct genus level with confidence 75 (0.75). By setting dada_min_boot to 60 (0.60) in this example, the reported assignment would be to the genus level. Users can adjust dada_min_boot based on their own observations concerning what threshold they begin to see inaccurate assignments.

This also contains a small commit to adjust the order of the read truncation parameters (truncq, trunc_qmin, trunc_rmin, trunclenf, trunclenr) in nextflow.config to match the order they appear in nextflow_schema.json. No functional difference.

[d4straub]

Thanks for contributing!
All fine to me, except the parameter documentation.

[zmudge3]

Those are great points! I renamed the "Taxonomic database" section to "Taxonomic assignment" and moved dada_min_boot into there. I put it at the top of that section, but feel free to move it lower if you think it needs it.

I found one link to that section (in usage.md) and updated the link.

[d4straub]

Great thanks!