build: update deployment for Docker

deploy/templates/Caddyfile.j2

@@ -0,0 +1,15 @@
+:80 :443 {
+    root * /srv
+    file_server
+
+    @proxy_paths {
+        not path /static/*
+    }
+
+    reverse_proxy @proxy_paths http://web:8000
+
+    log {
+        output stderr
+        format single_field common_log
+    }
+}