feat: support leaf bundles for blog posts, refactor header images

content/blog/2022-04-docker2caddy-reverse-proxy.md

@@ -8,8 +8,9 @@ tags:
   - fsfe
   - server
   - python
-headerimage: /blog/docker.jpg
-headercredits: Shipping a load of containers requires a reliable infrastructure
+headerimage:
+   src: /blog/docker.jpg
+   text: Shipping a load of containers requires a reliable infrastructure
 ---
 
 So you have a number of Docker containers running web services which you would