cmd/prune-contaiers: add a GC script for containers images

This script calls skopeo delete to prune image from a remote
directory. Currently only supports the FCOS tag structure.

If no duration is specified, no image will be pruned.

See coreos/fedora-coreos-tracker#1367
See coreos/fedora-coreos-pipeline#995

src/prune-containers

@@ -0,0 +1,12 @@
+#!/usr/bin/bash
+
+# 1 - list all tags from repo
+REGISTRY="quay.io/fedora-ostree-desktops/silverblue"
+
+TAGS_JSON=skopeo list-tags docker://${REGISTRY} | jq -r '.Tags[]'
+
+# 2 go through list and print date and stream
+for tag in $TAGS_JSON;
+do
+    echo $tag
+done