Show a warning when offloading items with queued upload tasks

[GianniCarlo]

Purpose

• Show a warning when offloading items with queued upload tasks, as the app won't be able to upload the file item if it's removed

Approach

• Show a confirmation alert prior to removing the backing file

Things to be aware of / Things to focus on

• I also included logic to merge queued sync tasks that only update metadata (most likely from playback), to avoid unnecessary multiple requests to the backend