fix: add the signup email confirmation env var (#458)

docker-compose.prod.yml

@@ -82,6 +82,9 @@ services:
       - SIGNUP_ALLOWED_DOMAINS=${SIGNUP_ALLOWED_DOMAINS}
       - SIGNUP_ALLOWED_EMAILS=${SIGNUP_ALLOWED_EMAILS}
 
+      # Sign-up email confirmation
+      - SIGNUP_EMAIL_CONFIRMATION=${SIGNUP_EMAIL_CONFIRMATION}
+
       # Gotenberg (Pdf generator)
       - GOTENBERG_URL=${GOTENBERG_URL}
       - GOTENBERG_DOCS_URL=${GOTENBERG_DOCS_URL}