Erroneous TMT label extraction logic

[fabianegli]

https://github.com/bigbio/sdrf-pipelines/blob/96e2a69faaa2e2636020f612bd7507d614460403/sdrf_pipelines/maxquant/maxquant.py#L78

Sorting the default label results in label_list being ['2', 'M', 'T', 'T'] with a length of 4 which then probably leads to leads being true and we have a 6-plex form a 2-plex.

I think the whole label extraction should be more stringent and fail on unknown input with a note that an issue should be opened in this repo to adjust for new labels (and fix bugs). Guessing could lead to issues that are hard to diagnose by users and errors might even go unnoticed.