feat: Add support for skipping processed files in transfer configs

- Introduce new `skip_processed_files` option for transfer configurations
- Add database migration to support the new column
- Update config form and UI to include skip processed files toggle
- Enhance scheduler to respect skip processed files setting
- Modify file processing logic to optionally skip previously processed files
- Add environment variable support for skip processed files configuration

go.mod

@@ -28,6 +28,7 @@ require (
 	github.com/google/uuid v1.3.0 // indirect
 	github.com/jinzhu/inflection v1.0.0 // indirect
 	github.com/jinzhu/now v1.1.5 // indirect
+	github.com/joho/godotenv v1.5.1 // indirect
 	github.com/json-iterator/go v1.1.12 // indirect
 	github.com/klauspost/cpuid/v2 v2.2.10 // indirect
 	github.com/leodido/go-urn v1.4.0 // indirect