Bust Cloudflare cache after docs deploy

After rsync, purge Cloudflare so docs.spring.io serves updated Antora
reference content without stale CDN responses.

Bump spring-doc-actions rsync-antora-reference to v0.0.22 to align with
bust-cloudflare-antora-cache and other spring-projects doc workflows.

Repository secrets (add under Settings → Secrets and variables →
Actions for spring-projects/spring-grpc):

- CLOUDFLARE_ZONE_ID — Cloudflare zone ID for the zone that fronts
  docs.spring.io (same convention as other spring-projects repos using
  spring-doc-actions).

- CLOUDFLARE_CACHE_TOKEN — Cloudflare API token with permission to
  purge cache for that zone (e.g. Cache Purge). These names match
  spring-security's deploy-docs workflow so existing org secrets may be
  reused if applicable.

Author: rwinch

.github/workflows/docs.yml

@@ -22,10 +22,16 @@ jobs:
       run: |
         ./build-docs.sh
     - name: Publish Docs
-      uses: spring-io/spring-doc-actions/rsync-antora-reference@v0.0.11
+      uses: spring-io/spring-doc-actions/rsync-antora-reference@v0.0.22
       with:
         docs-username: ${{ secrets.DOCS_USERNAME }}
         docs-host: ${{ secrets.DOCS_HOST }}
         docs-ssh-key: ${{ secrets.DOCS_SSH_KEY }}
         docs-ssh-host-key: ${{ secrets.DOCS_SSH_HOST_KEY }}
         site-path: spring-grpc-docs/target/antora/site
+    - name: Bust Cloudflare cache
+      uses: spring-io/spring-doc-actions/bust-cloudflare-antora-cache@v0.0.22
+      with:
+        context-root: spring-grpc
+        cloudflare-zone-id: ${{ secrets.CLOUDFLARE_ZONE_ID }}
+        cloudflare-cache-token: ${{ secrets.CLOUDFLARE_CACHE_TOKEN }}