[SQL/MEG] Add physiological_file.DownloadPath field

[MaximeBICMTL]

As discussed on Slack.

Problem

For the EEG data types that LORIS currently handles, the acquisition files are "real" files, which is very nice. However, for the MEG CTF data types, the acquisition files are actually directories. The BIDS specification says that these MEG CTF acquisitions must be stored as directories, not as archives, and the neuroscience libraries like MNE only work on directories. As such, it makes sense to store the MEG CTF as directories in the LORIS BIDS dataset. However, the users must also be able to download these acquisition files, which is problematic if those are directories.

Solution

Split physiological_file.FilePath into two fields FilePath (stays the same) and DownloadPath (new field):

• For "real" files, like those we currently have with EEG, the values of these fields are identical, as they both point to the same file.
• For directories, the FilePath field points to the directory in the BIDS dataset, and the DownloadPath points to an archive of that directory.

Whenever computation needs to be done in the dataset, the FilePath field is used, whenever the user wants to download an acquisition file, DownloadPath is used.

Testing

• ✅ Ran the patch on Raisinread.
• ✅ Looked for all occurences of physiological_file.FilePath in the electrophysiology_modules.
• ✅ Downloaded a main EEG acquisition file and its associated files, and confirmed that changing the DownloadPath to an invalid value only breaks the main file download.