Create SingleTableMetadata class

[amontanez24]

Problem Description

As a user, it would be helpful to have a class that I could interact with programmatically to handle all things related to single table metadata.

Expected behavior

• In the metadata module, we should add a class called SingleTableMetadata
• The class should have some private dict attribute that will store and keep track of the actual metadata for the class
• The __init__ requires no parameters
• There should be a to_dict method that returns the underlying json as a python dictionary

python_dict = metadata.to_dict()

• There should be an internal _load_from_dict class method that returns a SingleTableMetadata instance with the dictionary set to the dict provided

metadata = SingleTableMetadata._load_from_dict(dict)

• The __repr__ method should be overwritten so that when printed, the metadata class shows the underlying dictionary

>>> print(metadata)
{
    "columns": {
        "student_id": { "sdtype": "numerical" },
        "gender": { "sdtype": "categorical" },
        "gpa": { "sdtype": "numerical" },
        "age": { "sdtype": "numerical" },
        "education_level": { "sdtype": "categorical" }
      }
}