ci: only retain the 15 most recent images

.github/workflows/container-retention.yaml

@@ -0,0 +1,21 @@
+on: 
+  schedule:
+    - cron: "0 0 1 * *"
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+name: Prune Old Images
+env:
+  # Exclude LFS files
+  GIT_LFS_SKIP_SMUDGE: 1
+
+jobs:
+  prune:
+    runs-on: ubuntu-latest
+    name: 
+    steps:
+      - name: prune omakase-toolbox
+        uses: actions/delete-package-versions@v5
+        with:
+          package-name: 'omakase-toolbox'
+          package-type: 'container'
+          min-versions-to-keep: 15