Remove the rootfses from the package registry after 60 days

According to upstream two months is fine:
tianon: yeah, cleaning them out is reasonable, although I'd request that
they be available for something like 1-2 months after they're no longer
supported / "active"
tianon: in the case of something constantly changing like arch, 1 month
is probably pretty reasonable

Fix #57

.gitlab-ci.yml

@@ -2,6 +2,7 @@ default:
   image: "archlinux:latest"
 
 stages:
+  - cleanup
   - lint
   - rootfs
   - image
@@ -9,6 +10,23 @@ stages:
   - release
   - publish
 
+cleanup:
+  stage: cleanup
+  tags:
+    - secure
+  only:
+    refs:
+      - schedules
+    variables:
+      - $CLEANUP_PACKAGE_REGISTRY == "TRUE"
+  before_script:
+    - pacman -Syu --noconfirm jq
+  script:
+    - |
+      for id in $(curl --silent --fail --show-error "${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/packages?per_page=100&order_by=created_at&sort=asc" | jq '.[] | select(.created_at | split("T")[0] | . < (now-60*60*24*60|strflocaltime("%Y-%m-%d"))) | .id'); do
+        curl --silent --fail --show-error --request DELETE --header "PRIVATE-TOKEN: ${GITLAB_PROJECT_TOKEN}" "${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/packages/${id}"
+      done
+
 lint:
   stage: lint
   image: hadolint/hadolint:latest-alpine