Support for observationUnitLevelName for v2.0 GET /variables API

[abatac]

Is it possible to filter the variables associated to study by observationUnitLevelName in GET /variables?

In the Breeding Management System, a study may comprise multiple datasets used to group observations/sub-observations based on their levels. For instance, a dataset named "plot" includes observations for plot-level units, while a dataset named "plant" contains sub-observation units within each plot.

The challenge is that, despite belonging to the same study, each dataset in BMS can have a different set of observation variables.

Therefore, if I wish to retrieve variables specific to the "plant" dataset (level), it is not feasible to utilize the GET /variables?studyDbId=xxx endpoint, as it retrieves all variables within a study without providing a way to filter variables based on the observationUnitLevelName.

I know that this is a limitation in the Brapi spec, but this blocks the interoperability of Field-book with BMS BrAPI 2.0 implementation.

For example, If I import a Field via BrAPI using "plot" observation level, the traits retrieved from GET /variables?studyDbId endpoint will return all the variables in a study for all datasets (levels). Ideally, it should only return the variables based on studyDbId and observationUnitLevelName.

cc @BrapiCoordinatorSelby @mcrimi