log images to save_dir folder

[observingClouds]

This PR:

• logs the evaluation metric images to the save_dir folder instead of saving them in the current work directoty.
• it creates the save_dir if it does not exist

This PR is motivated by fixing an issue with DVC where the mlruns folder gets deleted for a new experiment to keep the environment clean. Saving the metric images to a separate folder helps to track these images also in DVC.

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[observingClouds]

This was not (yet) meant to be created here.