Add constraint methods to MultiTableSynthesizers

[amontanez24]

Problem Description

As a user, it would be convenient to be able to add constraints to individual table synthesizers in my multi-table dataset.

Acceptance Criteria

• Add wrapper methods to the BaseMultiTableSynthesizer for add_constraints and get_constraints.

Expected behavior

age_is_positive = {
  'constraint_class': 'Positive',
  'table_name': 'users',
  'constraint_parameters': {
    'column': 'age',
    'strict_boundaries': True
  }
}

my_custom_constraint = {
  'constraint_class': 'MyConstraintClass',
  'table_name': 'sessions',
  'constraint_parameters': {
    'custom_param_1': 34,
    'custom_param_2': True
  }
}

synthesizer.add_constraints(constraints=[age_is_positive, my_custom_constraint])

synthesizer.get_constraints()
[{
  'constraint_class': 'Positive',
  'table_name': 'users'
  'constraint_parameters': {
    'column': 'age',
    'strict_boundaries': True
  }
},
{
  'constraint_class': 'MyConstraintClass',
  'table_name': 'sessions',
  'constraint_parameters': {
    'custom_param_1': 34,
    'custom_param_2': True
  }
}]

Additional context

• Notice that the constraint dict in the multi-table case is slightly different than in the single table case because it contains table_name. The reason for not nesting the dictionaries under the table name is that future constraints might be between multiple tables.
• Test to make sure constraints other than Unique work

Error Case

MultiTableSynthesizers will not initially support the Unique constraint. If the user passes in any Unique constraint classes, throw an error.

unique_username = {
  'constraint_class': 'Unique',
  'table_name': 'users',
  'constraint_parameters': {
    'column': 'username',
  }
}

synthesizer.add_constraints(constraints=[unique_username])

SynthesizerInputError: Unsupported constraint class ('Unique'). Please remove the constraint for this synthesizer.