When an OM optin tracks a Conversion, push an event to GA account.

OptinMonsterTrackedConversion.js

jQuery(document).ready( function($) {
    $(document).on('OptinMonsterTrackedConversion', function( event, data, object ){
      dataLayer.push({
        'event': 'gaTriggerEvent',
        'gaEventCategory': 'form',
        'gaEventAction': 'submit',
        'gaEventLabel': 'optin-monster'
      });
    });
});