FEATURE: find a way to pre-compute the URL base path

[kpouget]

Currently when we export to MLFlow, the expe ID and run UUID are generated on the fly during the upload.

This prevents us from computing any URL during the test run, and the artifact URL is only known at the very last step of the pipeline.

Would be nice to have a way to negotiate with MLFLow the expe ID and run UUID that will be used for the final export, so that we can store the URL in the KPI (important), send a notification at the end of the run (less important, can be done after the artifact export)