Implement backend functionality for newsletter subscription and unsub…

…scription

- Added the ability to subscribe users to the newsletter, ensuring that email validation is performed.
- Implemented logic to handle resubscription for users who previously unsubscribed, generating a new unsubscribe token for them.
- Established an unsubscribe process that sets the subscriber's status to inactive while retaining the record in the database.
- Enhanced the database model to include an active status flag, which is updated based on subscription actions.
- Included comprehensive error handling for scenarios such as invalid email formats and expired tokens during unsubscribe requests.
- Updated the controller to handle subscription and unsubscription requests effectively, providing clear responses to the client.

These enhancements improve the overall user experience by providing seamless management of newsletter subscriptions.

src/main/resources/application-production.properties

@@ -14,3 +14,9 @@ spring.mail.password=${MAIL_SERVICE_PASSWORD}
 spring.mail.properties.mail.smtp.auth=${MAIL_SERVICE_SMTP}
 spring.mail.properties.mail.starttls.enable=${MAIL_SERVICE_STARTTLS}
 spring.mail.properties.domain_name=${MAIL_SERVICE_DOMAIN_NAME}
+
+# --- Oauth 2.0 Configurations ---
+spring.security.oauth2.client.registration.google.client-name=google
+spring.security.oauth2.client.registration.google.client-id=${YOUR_CLIENT_ID}
+spring.security.oauth2.client.registration.google.client-secret=${YOUR_SECRET_KEY}
+spring.security.oauth2.client.registration.google.scope=email,profile