Request: expose Experiment._modelDirectory

Hi all,

In AutoML, when configuring the `ExperimentSettings`, one can set a `CacheDirectory` where the intermediate models will be stored. However, the models are actually stored in a subfolder, called "ExperimentXX", where XX in an auto-increment integer in v.0.14.0, and some random characters in the recent preview releases. Navigating the source code, I found that this path is stored inside the private readonly field `_modelDirectory` belonging to the internal class `Experiment`. When running many experiments, there is no way to associate each experiment to each subfolder.
In my scenario, caching is necessary due to dataset size, and I would like to delete the temporary models at the end of the experiment without bothering other experiments that may be running simultaneously.

Thanks