chore(config,notification_queue): externalize notification template names to environment variables

fix(notification_queue): update password reset template name from otp_verification to otp

fix(notification_queue): update password reset template to use otp_verification

feat(notification-templates): add notification template management module

refactor(notifications): migrate to MongoDB-backed notification queue with Fast2SMS integration

passing employee_user_id to create_user function

feat(notifications): implement queue-based notification system with multi-channel support