Add TRUST_PROXY env var for reverse-proxy deployments

Fixes express-rate-limit's ERR_ERL_UNEXPECTED_X_FORWARDED_FOR warning
and incorrect IP keying when nginx runs on a separate server in front
of the app.

backend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "event-management-backend",
-  "version": "1.9.3",
+  "version": "1.9.4",
   "description": "Event Management System Backend",
   "main": "src/index.js",
   "scripts": {