Include foreign references when validating dependencies

[tvogels01]

Summary

When we validate the depends_on field in table design files, we should consider that some columns have an explicit foreign reference. These references should be allowed into the depends_on field. Currently, the dependencies are coming only from the transformation's SQL.

Details

A/C

• Foreign key references (on columns) are validated (does the column actually exist?)
• Foreign tables are added to depends_on