Behavior of .push_to_dir() and .from_dir()

[kasperjunge]

Currently, the "push_to_dir()" method in the PromptFunction pushes a JSON file with the completion config to a specified directory. If a new or modified version of the PromptFunction is pushed to the same directory, it simply overwrites the existing file.

However, to enhance the ability to track prompt experiments, it would be beneficial to incorporate built-in versioning into the push/pull functionality. This could be achieved by utilizing the value generated by "CompletionConfig().unique_hash()".

The DirectoryPushPullMixin controls the directory push/pull logic.

I'd appreciate any suggestions on how this could be implemented.