Support entity definition TSV files

[tsalo]

Your idea

In #1613, we added a descriptions.tsv file to the Derivatives spec. The file describes different desc-<label> definitions used in a dataset. I believe this general structure can be applied to other entities, especially acq-<label> (acquisitions.tsv), rec-<label> (reconstructions.tsv), proc-<label> (processings.tsv?), and recording-<label> (recordings.tsv).

[sappelhoff]

I believe this general structure can be applied to other entities

This is in fact, how the idea for descriptions.tsv originated when we discussed in in Copenhagen 2023. There are some minor inconsistencies, like participants.tsv, which should rather have been subjects.tsv (corresponding to the sub entity).

I am generally in favor of adding support like this wherever it is practically meaningful (that is, if we see a concrete use case).