Add dotenv support and bulk SMS endpoint

- Integrated dotenv for environment variable management.
- Updated queueWorker to use WORKER_INTERVAL from .env or default to 5 seconds.
- Added a new bulk SMS endpoint to queue multiple messages in a single request, with validation and transaction handling.
- Updated package.json and package-lock.json to include dotenv dependency.

server.js

@@ -1,3 +1,4 @@
+require('dotenv').config();
 const express = require('express');
 const http = require('http');
 const socketIo = require('socket.io');