Add add_constraint method to MultiTableMetadata

[amontanez24]

Problem Description

As a user, it would be very useful to be able to add constraints for a table programmatically to my MultiTableMetadata.

Expected behavior

• Add add_constraint method
  • This should just call the single table add_constraint method for the specified table
  • Parameters
    • table_name: string that is the name of the table
    • constraint_name: string that is the name of the constraint class
    • **kwargs: Any other required key word arguments for the constraint.
  • Errors:
    • Same as single table
    • If the table doesn't exist, raise an error
      Error: Unknown table name ('userss')

>>> metadata.add_constraint(
        table_name='users',
        ...)

>>> metadata.add_constraint(table_name='userss', ...)
Error: Unknown table name ('userss')

>>> metadata.add_constraint(
        table_name='users',
        constraint_name='Inequality',
        low_column_name='child_age',
        high_column_name='start_date')
Error: An Inequality constraint is being applied to mismatched sdtypes ("child_age", "start_date"). Both columns must be either numerical or datetime.