Add rate limiter to POST /api/products

[deepak30012004]

title: Add express-rate-limit to POST /api/products route

summary: |
This PR adds rate limiting to the POST /api/products endpoint using the
express-rate-limit package to prevent abuse and ensure API stability.

what_i_did:

• Installed express-rate-limit via npm install express-rate-limit.
• Configured a rate limiter to allow 5 requests per minute per IP.
• Applied the rate limiter only to the POST /api/products route in index.js.

why: |
To:

• Prevent spam or abuse of the product submission route.
• Improve backend security.
• Demonstrate use of security middleware as part of good API practices.

how_to_test:

• Run npm install.
• Start the server with node index.js.
• Use Postman or curl to send more than 5 POST requests to /api/products within 1 minute.
• After the 5th request, you should receive a 429 response with the custom error message.

future_suggestions:

• Switch to Redis-based rate limiter for distributed systems or production environments.
• Apply rate limiting globally or to other sensitive endpoints as needed.
• Allow authenticated users to have a higher request quota.
• 👉 If you want to make more requests per minute:
  • Increase the max value in the rate limiter configuration.
  • Contact the admin or implement a premium tier with higher limits.
  • Use API keys or user roles to set dynamic rate limits.

note: Let me know if you'd like me to help implement any of these in the next PR!