Specifying column attributes in `upload_entities`

[SHuang-Broad]

Hi,

I may need a feature that is currently probably un-supported by FISS.
I am willing to add that feature by a PR, but just need a pointer on where to start.
One caveat is that I am unsure if the Terra API supports this (if not, then this ticket should be opened there).

Currently fapi.help() describes upload_entities as

    upload_entities(namespace, workspace, entity_data, model='firecloud')
        Upload entities from tab-delimited string.
        
        Args:
            namespace (str): project to which workspace belongs
            workspace (str): Workspace name
            entity_data (str): TSV string describing entites
            model (str): Data Model type. "firecloud" (default) or "flexible"
        
        Swagger:
            https://api.firecloud.org/#!/Entities/importEntities
            https://api.firecloud.org/#!/Entities/flexibleImportEntities

Where entity_data is treated basically as a flat string type.

What I am trying to get to, is to support specifying the column attributes when uploading the table through FISS, like in this screenshot via Terra GUI

Thanks!
Steve