update things.fmriprep repo and install as a submodule

[MarieStLaurent]

• I can't seem to locate the things.fmriprep repo on the cneuromod github (is it private?). I do have an older version installed under projects/rrg-pbellec/mstlaure/things_memory_results/data/things.fmriprep which I used for analyses, though. Could you validate that the things.fmriprep repo is accessible publicly on github?
• MARIE TODO: once I can access the repo, validate that the final scans are consistent with the corrections documented in the text file under THINGS/fmriprep/sourcedata/things/code/cleanup/qc_notes.md. E.g., sub-06, ses-008, run 6 was misaligned and removed from the analysis but is it still in the repo?
• Make sure that, on its main branch, the things.fmriprep repo has a submodule sourcedata/things that points toward the latest cneuromod.things main branch updated to include code, corrected events files and eyetracking files, and that is links to the latest things.stimuli repo branch that includes annotations.
• Install things.fmriprep as a submodule called fmriprep under cneuromod-things/THINGS to replace the fmriprep placeholder directory.