message: also add dynamic backend to default varnish config.
diff: vcl 4.0;
  import std;
  +import dynamic;
  # set backend default
  backend default {
  @@ -20,6 +21,14 @@ backend default {
  .between_bytes_timeout = 10m;
  }
  +sub vcl_init {
  + new www_dir = dynamic.director(
  + port = "${VARNISH_BACKEND_PORT:-8080}",
  + first_byte_timeout = 90s,
  + between_bytes_timeout = 90s,
  + ttl = 60s);
  + }
  +
  sub vcl_recv {
  # Happens before we check if we have this in cache already.
  #
  