Default MLFlow tracking cannot set if tracking the config artifacts

[binliunls]

Is your feature request related to a problem? Please describe.
When running a typical MONAI model zoo bundle training with tracking="mlflow", it will always try to record all the config files as artifacts due to this line. If the execute_config is set, it will track config files in the specific path. When the execute_config parameter is not set it will track the default path.

Describe the solution you'd like
The execute_config parameter should be a bool| string type, so that users can set it as False, if they do not want to record any configs. They can set the parameter to True to record the default path or to a real path if config files are saved in other places.