Add drf-commons to third-party packages documentation

[htvictoire]

Package: drf-commons
PyPI: https://pypi.org/project/drf-commons/
Repo: https://github.com/htvictoire/drf-commons
Docs: https://drf-commons.readthedocs.io

drf-commons is a production-grade utility library for Django REST Framework
that addresses structural gaps not covered by DRF out of the box:

• Composable model mixins (UUID PK, soft delete, optimistic locking, audit trail)
• Pre-composed ViewSet classes including BulkViewSet and ImportableViewSet
• 20+ configurable serializer field types (IdToDataField, FlexibleField, etc.)
• Async-safe current user resolution via ContextVar (ASGI compatible)
• Standardized response envelopes with ISO8601 timestamps
• CSV/XLSX/PDF import and export services
• Structured logging and SQL debug middleware

Available on PyPI: pip install drf-commons