Add support for dbt-spark optional configs

[felipe-curebase]

I have a valid dbt-spark project where I'm configuring global optional properties for models, seeds and snapshots (+file_format: delta) in dbt_project that are failing to validate.

[joellabes]

Thanks @felipe-curebase - if you wanted to open a PR that adds these, and calls out in the Description field that they're Spark/Redshift only, that would be grand 🌟

[dave-connors-3]

hey @felipe-curebase ! are you still seeing this issue? I see we have a file_format key in each of our dbt_project.yml schemas currently! testing locally, the current schemas seem to validate properly