fix: Fix and rename pg_database_url.sh helper script (#2747)

- Fix and rename pg_database_url helper script
- Use single-quote and remove trailing whitespace

docker/entrypoints/rails.sh

@@ -10,7 +10,7 @@ echo "Waiting for postgres to become ready...."
 
 # Let DATABASE_URL env take presedence over individual connection params.
 # This is done to avoid printing the DATABASE_URL in the logs
-$(docker/entrypoints/helpers/pg_database_url.sh)
+$(docker/entrypoints/helpers/pg_database_url.rb)
 PG_READY="pg_isready -h $POSTGRES_HOST -p $POSTGRES_PORT -U $POSTGRES_USERNAME"
 
 until $PG_READY