Create a DBML exporter

[cmungall]

DBML docs
https://dbml.dbdiagram.io/home

Technically we don't need to write any code here - we export and import to SQL so we could just add docs on how to chain tools together

But in practice it might be nice to have a one-stop command that will generate DBML directly

There is no driving requirement here as I think we have visualization tools well covered, but opening this as it may be a good first issue for someone

Note that DBML is used by a lot of genomics projects like GREGOR/PRIMED, but it looks like their authoring workflow is sheets->custom json [analogous to schemasheets] and then json->dbml->viz

e.g. https://github.com/UW-GAC/primed_data_models/blob/main/json_to_dbml.R