Allow me to create a custom constraint class and use it in the same file

[npatki]

Problem Description

The current API assumes that the custom constraint class is defined a Python file, and then imported/created in a different Python file. I would like the option to create a class and use it in the same file

This also makes demoing & internally testing a custom constraint a lot easier.

Expected behavior

In the new SDV 1.0 API, the workflow is changing a bit. When loading a constraint class from a different file, we will offer this function:

synthesizer.load_custom_constraint_classes(
    filepath='my_custom_constraint.py',
    class_names=['MyCustomConstraint'])

When you want to do it from the same file, you will have the object. We should add a new function to add it.

synthesizer.add_custom_constraint_class(
    class_object=MyCustomConstraint,
    class_name='MyCustomConstraint' # the name to use when referring to the constraint
)

Then you can create constraints using the defined class_name:

constraint = {
  'constraint_class': 'class_name',
  'constraint_parameters': {
    'column_names': ['A', 'B'],
    'my_custom_parameter': 10
  }
}