- What I did

Added Prometheus counters to track image deletion success and failures. This complements the timer metrics added in#47555 by providing counters for monitoring deletion operations.

- How I did it

• Added two new metrics indaemon/internal/metrics/metrics.go:
  • ImageDeletesCounter: Tracks successful deletions
  • ImageDeletesFailedCounter: Tracks failed deletions with categorized reasons
• Updated both containerd (daemon/containerd/image_delete.go) and graphdriver (daemon/images/image_delete.go) backends
• Created error categorization function that classifies failures into:not_found,conflict,permission_denied,invalid_argument, orunknown
• Added unit tests for error categorization in both backends

- How to verify it

1. Start Docker daemon with Prometheus metrics enabled
2. Perform image deletion operations (both successful and failing cases)
3. Check metrics endpoint (typicallyhttp://localhost:9323/metrics):

   # Successful deletionengine_daemon_image_deletes_total# Failed deletions by reasonengine_daemon_image_deletes_failed_total{reason="conflict"}engine_daemon_image_deletes_failed_total{reason="not_found"}

4. Run unit tests:go test ./daemon/containerd/... ./daemon/images/... -run TestCategorizeImageDeleteError

- Human readable description for the release notes

Add Prometheus counters for image deletion operations (`engine_daemon_image_deletes_total` and`engine_daemon_image_deletes_failed_total{reason}`) to track success/failure rates and categorize deletion errors.

- A picture of a cute animal (not mandatory but encouraged)

🐳