Delete unused images

Filters to process on the prune list, encoded as JSON (a map[string][]string). Available filters:

• dangling=<boolean> When set to true (or 1), prune only unused and untagged images. When set to false (or 0), all unused images are pruned.
• until=<string> Prune images created before this timestamp. The <timestamp> can be Unix timestamps, date formatted timestamps, or Go duration strings (e.g. 10m, 1h30m) computed relative to the daemon machine’s time.
• label (label=<key>, label=<key>=<value>, label!=<key>, or label!=<key>=<value>) Prune images with (or without, in case label!=... is used) the specified labels.