Salesforce: Add option to submit form data asynchronously

Description

Provide an option to allow for asynchronous submission of data to Salesforce. This includes adding a checkbox on the admin settings screen to enable async.
If this option is enabled, data submission is a "fire and forget" operation. That is, we won't get back the entityId and store it in the mai cookie. Therefore, auto-fill and personalization based on Salesforce fields won't work.