refactor: remove SSL from standalone setup

Since Zeppelin was only creating a self-signed certificate, this
gave a false sense of security when in reality you'd always want
to have a proxy with a proper certificate in front of this anyway.

Additionally, generating the certificate at build time meant that
the domain couldn't easily be changed/updated without rebuilding.

docker-compose.standalone.yml

@@ -28,10 +28,8 @@ services:
     build:
       context: .
       dockerfile: docker/production/nginx/Dockerfile
-      args:
-        STANDALONE_DOMAIN: ${STANDALONE_DOMAIN:?Missing STANDALONE_DOMAIN}
     ports:
-      - "${STANDALONE_WEB_PORT:?Missing STANDALONE_WEB_PORT}:443"
+      - "${STANDALONE_WEB_PORT:?Missing STANDALONE_WEB_PORT}:80"
 
   migrate:
     depends_on: