fixes https://github.com/aenix-io/cozystack/issues/602
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## Summary by CodeRabbit
- **New Features**
- Introduced a new custom assets server for serving static files
- Replaced `darkhttpd` with a custom Go-based file server
- **Improvements**
- Updated base images to Alpine Linux 3.21
- Simplified container dependencies
- Enhanced server configuration with command-line flags
- **Infrastructure**
- Rebuilt Kubernetes deployment configuration for assets service
- Updated server startup parameters and container settings
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