Add additions support

deployment/caddy/Dockerfile

@@ -10,4 +10,23 @@ RUN xcaddy build \
 FROM caddy:2
 
 COPY --from=builder /usr/bin/caddy /usr/bin/caddy
-COPY Caddyfile /etc/caddy/Caddyfile
+COPY Caddyfile /etc/caddy/Caddyfile
+COPY additions /etc/caddy/additions
+
+# Merge base Caddyfile + additional snippets (if present),
+# in alphabetical order, and remove additions from final image.
+RUN sh -c 'set -eu; \
+  if [ -d /etc/caddy/additions ]; then \
+    tmp="$(mktemp)"; \
+    cat /etc/caddy/Caddyfile > "$tmp"; \
+    for f in $(printf "%s\n" /etc/caddy/additions/* 2>/dev/null | sort); do \
+      [ -f "$f" ] || continue; \
+      base="$(basename "$f")"; \
+      [ "$base" = ".gitkeep" ] && continue; \
+      [ "$base" = ".gitignore" ] && continue; \
+      printf "\n\n" >> "$tmp"; \
+      cat "$f" >> "$tmp"; \
+    done; \
+    mv "$tmp" /etc/caddy/Caddyfile; \
+    rm -rf /etc/caddy/additions; \
+  fi'

deployment/caddy/additions/.gitignore

@@ -0,0 +1,2 @@
+*
+!.gitignore