Validate emails before sending

[abhitrueprogrammer]

Use https://github.com/devmehq/email-validator-js to validate emails before sending proceeding to proceeding to send them to google sheets (sending them to google sheets is already done.

backend: https://github.com/CodeChefVIT/papers-codechef/blob/subscribe-to-newsletter-button/src/app/api/subscribe/route.ts

frontend: https://github.com/CodeChefVIT/papers-codechef/blob/subscribe-to-newsletter-button/src/components/Footer.tsx