fix(elixir): file upload in production

- move uploads to new directory (`./uploads` per default)

docker-compose.yml.example

@@ -25,9 +25,12 @@ services:
       PHX_HOST: "localhost"
       PHX_SERVER: "true"
       PORT: "4000"
+      UPLOADS_DIR: "/data/uploads"
     depends_on:
       db:
         condition: service_healthy
+    volumes:
+      - uploaded_files:/data/uploads
     command:
       [
         "/bin/sh",
@@ -37,3 +40,4 @@ services:
 
 volumes:
   postgres_data:
+  uploaded_files: