add anat.smriprep submodule

[MarieStLaurent]

Note: I did install a submodule already as cneuromod-things/anatomical/smriprep but I kind of messed it up with the branches and submodules. Might be simpler to remove and reinstall it cleanly... (with correct branch pointing to updated anat.freesurfer submodule)

• Within the CNeuroMod anat.smriprep repo, on the main branch, update the sourcedata/freesurfer submodule so that it points to the main branch of the anat.freesurfer repo's main branch (AFTER the flat_patch branch has been merged into main).

• Under cneuromod-things/anatomical, replace the current smriprep submodule with a new one that it points to the updated anat.smriprep repository (main branch) with the latest freesurfer submodule.