Create example phenotypic inputs for no-session-layer BIDS case

[alyssadai]

At the moment, we have tests which check that:

• A custom PhenotypicSession called ses-unnamed is created by the bagel pheno command when it receives a phenotypic TSV with missing session column values
• A custom ImagingSession called ses-unnamed (that has pipeline metadata) is created by the bagel derivatives command when it receives a proc status TSV w/ missing session column values
• The session file path stored by bagel bids for a BIDS subject missing a session layer points to the BIDS subject directory (i.e., instead of inserting a fake session directory layer)

What we don't have:

• A test of the bagel bids command that checks that when a BIDS directory with no session layer is provided, the output JSONLD file contains at least one ImagingSession called ses-unnamed, where the file path for the session still points to the subject directory

This would test, explicitly, that ses-unnamed ImagingSessions are correctly created from BIDS datasets without sessions, and that the same sessions still have accurate paths to the data. At the moment, the combination of existing tests can be argued to test this implicitly.

To be able to create the above test, we would need:

1. A BIDS dataset with no session layer (e.g., ds001 or eeg_ds000117 from `bids-examples)
2. A custom phenotypic JSONLD to provide as input to bagel bids, that includes all subjects in the BIDS dataset above
3. In order to generate 2., we would need to create:
   a. a new valid phenotypic TSV with all subjects in the missing-session-layer BIDS dataset
   b. a corresponding valid Neurobagel data dictionary JSON

Add to tests/data:

• example_no_session.tsv
• example_no_session.json

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[alyssadai]

@surchs I'm rereading this issue I created (quite a while ago) and would like a second opinion on whether this is still worth addressing.

What gives me pause is the potential overhead related to adding these new examples: we will either need a test that runs both the bagel pheno and bagel bids commands, which seems kind of complex, or a new example JSONLD corresponding to another bids-examples dataset (one missing sessions) that we will have to maintain.

Wdyt? Do you think the intended handling of missing sessions in BIDS data is sufficiently covered by existing tests?