Add add_relationship method to MultiTableMetadata

[amontanez24]

Problem Description

As a user, it would be helpful to be able to programmatically specify and add relationships between tables in my metadata.

Expected behavior

• Add a add_relationship method
• The relationship should be added to the private dict created in Create MultiTableMetadata class #883
• Parameters:
  • parent_table_name: A string representing the name of the parent table
  • child_table_name: A string representing the name of the child table
  • parent_primary_key: A string or tuple of strings representing the primary key of the parent
  • child_foreign_key: A string or tuple of strings representing the foreign key of the child
• Errors:
  • Check for the same errors as described in Add validate method to MultiTableMetadata #888

metadata.add_relationship(
  parent_table_name='users',
  child_table_name='transactions',
  parent_primary_key='user_id', # can be a tuple for composite keys
  child_foreign_key='purchaser_id' # can be a tuple for composite key
)

metadata.add_relationship(
  parent_table_name='users',
  child_table_name='transactions',
  parent_primary_key='user_id', # can be a tuple for composite keys
  child_foreign_key='start_date' # can be a tuple for composite key
)
Error: Relationship between tables ('users', 'transactions') is invalid. The primary and foreign key columns are not the same type.