feat(ci): purge CDN cache after process-updates runs

process_cran_updates uploads fresh PACKAGES* to S3, but the CDN was only
purged by the daily update-package-index-* chain.
Between the two cron runs, edges kept serving the stale index,
so a binary that had just landed in S3 was effectively invisible
until the next index-update purge.

Adds the same purge step that update-package-index-* already uses,
parameterized per platform/arch.

.crow/process-updates-redhat-8-amd64.yaml

@@ -75,3 +75,17 @@ steps:
             operator: 'Equal'
             value: 'true'
             effect: 'NoSchedule'
+
+  - name: Purge CDN cache
+    image: reg.devxy.io/docker.io/library/alpine:3.23
+    environment:
+      BUNNYNET_API_KEY:
+        from_secret: BUNNYNET_API_KEY
+      SUBDOMAIN1: 'cran.devxy.io'
+      SUBDOMAIN2: 'cran.allianceswisspass.devxy.io'
+      SUBDOMAIN3: 'cran.rpkgs.com'
+      OS_ID: rhel8
+      ARCH: amd64
+    commands:
+      - apk add --no-cache -q bash curl
+      - bash scripts/purge_cdn_cache.sh "$BUNNYNET_API_KEY" "$ARCH" "$OS_ID" "$SUBDOMAIN1" "$SUBDOMAIN2" "$SUBDOMAIN3"