Automatic Extraction of OpenWrt Firmware Image Metadata

OpenWISP Firmware Upgrader currently requires users to manually enter metadata when uploading firmware images, which is error prone and doesn't scale. This project adds automatic metadata extraction that runs as a background Celery task on upload, using fwtool as the primary method and DTB parsing as a fallback, with graceful handling for images that support neither. A draft/confirmed state machine keeps unverified images invisible to the upgrade system until extraction succeeds or an operator manually confirms the metadata. The implementation follows the existing upgrader class pattern for extensibility, includes full test coverage using real OpenWrt images, and adds build-level status aggregation with notifications.