Ignore tables during generation

[piercefreeman]

If you have other non-iceaxe tables that are under local management, our generation commands will always try to drop them because it assumes the data models have just been deleted. This PR allows users to override this when implementing the CLI commands:

 await handle_generate(                                                                                                                                   
      "my_project",                                                                                                                                        
      db_connection,                                                                                                                                       
      ignore_tables=["table_to_skip", "another_table"]                                                                                                     
  )