feat: Add multi-threaded file transfers and enhanced logging support

- Implement concurrent file transfer processing with configurable concurrency
- Add new `max_concurrent_transfers` column to transfer configurations
- Enhance scheduler to support multi-threaded file transfers
- Introduce advanced logging system with rotation and configurable log levels
- Update Docker Compose and documentation with new logging configuration options
- Modify directory structure to separate data, backups, and logs
- Add environment variables for comprehensive logging control
- Improve error handling and logging in file transfer processes

internal/db/migrations/migrations.go

@@ -12,6 +12,7 @@ func InitMigrations(db *gorm.DB) *gormigrate.Gormigrate {
 		AddDeleteAfterTransferColumn(),
 		AddCloudStorageFields(),
 		AddSkipProcessedFilesColumn(),
+		AddMaxConcurrentTransfersColumn(),
 	}
 
 	return gormigrate.New(db, gormigrate.DefaultOptions, migrations)