Caddy: Move to more templated approach

no ref

- The goal here is to be able to provide more functionality to self-hosters through snippets and other segmented config
- Some customers run Admin <-> content domains on separate ones which our current config doesn't support
- Our current config also hardcodes a www redirect which complicates setups when you don't have that domain setup or don't even want it
- Moving to a default template customers will have to copy which includes snippets allows us to update these later on without breaking peoples setups

compose.yml

@@ -9,8 +9,9 @@ services:
       - "443:443"
     environment:
       DOMAIN: ${DOMAIN:?DOMAIN environment variable is required}
+      ACTIVITYPUB_TARGET: ${ACTIVITYPUB_TARGET:-https://ap.ghost.org}
     volumes:
-      - ./Caddyfile:/etc/caddy/Caddyfile
+      - ./caddy:/etc/caddy
       - caddy_data:/data
       - caddy_config:/config
     depends_on: