After onboarding fires newfold/onboarding/completed, we'll check if the user has interacted/opted-in. If they didn't, we'll disable the coming soon and set a timestamp.

This PR also exposes the 'last changed timestamp' value in both the container's service provider and the JS API.

Example

Service Provider:

$coming_soon_service = container()->get( 'comingSoon' );
$coming_soon_service->get_last_changed_timestamp(); // returns Unix timestamp
// or 
$coming_soon_service->get_last_changed_timestamp( true ); // returns date formatted timestamp

JavaScript API:

await NewfoldRuntime.comingSoon.lastChanged(); 
// returns date formatted timestamp, false if empty or null on error

This PR addresses part of this internal ticket: https://jira.newfold.com/browse/PRESS2-1505