Feat: Add the migration script and its doc, added `backup` as default… (#8245)
### What problem does this PR solve?
This PR adds a data backup and migration solution for RAGFlow Docker
Compose deployments. Currently, users lack a standardized way to backup
and restore RAGFlow data volumes (MySQL, MinIO, Redis, Elasticsearch),
which is essential for data safety and environment migration.
**Solution:**
- **Migration Script** (`docker/migration.sh`) - Automates
backup/restore operations for all RAGFlow data volumes
- **Documentation**
(`docs/guides/migration/migrate_from_docker_compose.md`) - Usage guide
and best practices
- **Safety Features** - Container conflict detection and user
confirmations to prevent data loss
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
- [x] Documentation Update
Co-authored-by: treedy <treedy2022@icloud.com>
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