Write out `acq` entity modifications to an `acquisitions.tsv` file

[tsalo]

Summary

When CuBIDS modifies files' acq entities, it should also describe the associated groupings in an acquisitions.tsv file. If one already exists, the original acq's entry should be copied and added to with the modifications.

Additional details

This is related to bids-standard/bids-specification#1706.