Improve code organization in object_storage.rb

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🔥 Problem

Follow up from !106740 (comment 1353947461).

app/uploaders/object_storage.rb contains most of the logic that is executed during file uploads. That file is quite complex to read and to reason about.

🚒 Solution

• We have multiple classes, modules in the same single file. Split each classe/module in its own file.
• Use override to clearly flag carrierwave functions overrides.