Function enqueue_upload 

async fn enqueue_upload(
    profile_id: ProfileId,
    bucket: BucketId,
    key: String,
    source_path: PathBuf,
    queue: &TransferQueueHandle,
    client: Arc<Client>,
    lock_registry: Arc<LockRegistry>,
    multipart_table: Arc<MultipartTable>,
    log: NotificationLogHandle,
    settings: SettingsHandle,
    channel: AppHandle,
) -> Result<String, AppError>

Register and spawn an upload task. Returns the new request_id.