cache.py

Added description composer backend

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/183512



Merged-by: Radamanthus Batnag <rbatnag@gitlab.com>
Approved-by: Jeff Park <jpark@gitlab.com>
Approved-by: Radamanthus Batnag <rbatnag@gitlab.com>
Approved-by: Alex Buijs <abuijs@gitlab.com>
Reviewed-by: Radamanthus Batnag <rbatnag@gitlab.com>
Co-authored-by: Phil Hughes <me@iamphill.com>