Ensure consistent dynamic module path for custom components

[neo]

What does this PR do?

Currently the behaviour/final module path of the are different in the following way:

• if it's a standalone custom AutoModel, the dynamic module is being loaded directly from the hub into diffusers_modules.local.org--repo.hash.file.class
• however if it's a custom component from a pipeline, hub files were already downloaded and cached from previous loading, and it's being passed as a "local dir", thus the dynamic module becomes diffusers_modules.local.file.class

This proposed change is to unify the second behaviour to be consistent with the first one where if it's being loaded from a local dir that's known to be a hub download cache; and as a bonus, it's more self contained and less likely to collide with other custom modules with the same file name sharing in the same local diffusers_modules.root folder/module

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• git blame author: @patrickvonplaten
• General functionalities: @sayakpaul @yiyixuxu @DN6