Add task content information on dataset cards

[Remi-Gau]

Users who want to look for task data (fmri for now, but could be eeg, meg...) may benefit from having the card of each dataset display the list of task they contain, possibly with extra metadata associated with them (TaskDescription, Instructions...).

It would also be beneficial to also include this as a search field.

As a first pass I think most users would not mind if you could not tell them exactly that this subject 1 has task X, Y, Z but subject 2 has only task X (I also believe this will be a rare case in most datasets), but allowing to see and possibly search task information at least at the dataset level would be a plus.

[github-actions]

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