Add add_constraint method to SingleTableMetadata

[amontanez24]

Problem Description

As a user, it would be very useful to be able to add constraints to the metadata programmatically since some of them often get missed the first time around.

Expected behavior

• Add add_constraint method
  • This should add the constraint info to the dict
  • Parameters
    • constraint_name: string that is the name of the constraint class
    • **kwargs: Any other required key word arguments for the constraint.

>>> metadata.add_constraint(
        constraint_name='FixedIncrements',
        column_name='salary',
        increment=5000)

# we should do a validation when they add this
>>> metadata.add_constraint(
        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.

Additional context

• For validation and error handling use the _validate_inputs method made in Add _validate_inputs class method to each constraint #878 and in Add validate method to SingleTableMetadata #879