Add update_column and add_column methods to SingleTableMetadata

[amontanez24]

Problem Description

As a user, it would be helpful to be able to modify or add to the metadata programmatically.

Expected behavior

• Add update_column method
  • Not all fields are required. Just update the ones provided in the SingleTableMetadata's dict
  • Parameters:
    • column_name: string that is the name of the column to update
    • **kwargs: any key word arguments that describe metadata for a column
  • Errors:
    • If the column doesn't already exist in the metadata raise the following error
      Error: Column name ('ssnn') does not exist in the table. Use 'add_column' to add new columns.
    • Run all of the column validations that are done in the validate method. eg. Add validate method to SingleTableMetadata #879
      Error: Invalid values ("pii") for numerical column "age".

>>> metadata.update_column(column_name='ssn', pii=True)
>>> metadata.update_column(
         column_name='education',
         order=['hs', 'bachelor', 'masters', 'PhD'])

• Add add_column method
  • All required parameters for the column metadata must be provided
  • Parameters:
    • column_name: string that is the name of the column to update
    • **kwargs: any key word arguments that describe metadata for a column
  • Errors:
    • If the column already is in the metadata, raise the following error:
      Error: Column name 'user_id' already exists. Use 'update_column' to update an existing column.
    • Run all of the column validations that are done in the validate method. eg.
      Error: Invalid values ("pii") for numerical column "age".
Error: Invalid values ("pii") for numerical column "age".

>>> metadata.add_column(column_name='cell', sdtype='phone_number', pii=True)