add build script for render backend deployment

backend/build.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+# exit on error
+set -o errexit
+
+echo "Installing the latest version of poetry..."
+pip install --upgrade pip
+pip install poetry==1.4.1
+
+rm poetry.lock
+poetry lock
+python -m poetry install