Enable artifact logging for mlflow logger
🚀 Feature
mlflow provides the ability to log artifacts (a local file or directory). However, the MLFlowLogger class does not have the wrapper method for this functionality.
Motivation
I always use the log_artifacts method of mlflow to log things like the last weights file for the run, confusion matrix image for the last set of weights, etc. It would be great to have these features integrated with the lightning logger.
Pitch
I'm currently using the mlflow logger and not the pytorch lightning's MLFlowLogger class but having this functionality would make the migration better.
Additional context

https://www.mlflow.org/docs/latest/python_api/mlflow.html#mlflow.log_artifact
https://www.mlflow.org/docs/latest/python_api/mlflow.html#mlflow.log_artifacts
https://www.mlflow.org/docs/latest/concepts.html#referencing-artifacts