allow multiple inputs in boutiques_bids_single_subject_maker, and/or arbitrary prefixes to bids subjects folder names

[MontrealSergiy]

• The boutiques_bids_single_subject_maker.rb mod(ule) changes a regular bids boutiques into one that consumes bids subject folders rather than bids datasets. Yet dataproviders typically allow only one folder (collection) with same name, which complicates hosting several datasets on the same dataprovider. Besides the main dataset, some might like to keep cleaned-up, derivative, p recomputed data, different version etc. Therefore I suggest to allow bids single subj folders have prefixes reflecting e.g. dataset name, previously, applied workflow, or original folder structer, e.g opni-sub-01, hbcd-sub-xyz .
• Another relaxing suggestion is make name of synthetic/mock/singleton bids folder parameterized. Suggestion target tools consuming 2 bids datasets (e.g. when combining several tools, passing precomputed intermediate results from one tool to another). A less generic alternative is to give a predefined name to seconds bids dataset that changes with index, e.g. BIDSDATASET_2, or appends input name to it something like (BIDSDATASET_input_1)

Either suggestion could be either new mod or update of the current Single Subject.

[MontrealSergiy]

see also Erik's today emails from 10 30