Added iframe CSP headers with configuration via .env. Updated session cookies to be lax by default, dynamically changing to none when iframes configured to allow third-party control. Updated cookie security to be auto-secure if a https APP_URL is set. Related to #2427 and #2207.  | 
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| Controllers | ||
| Middleware | ||
| Requests | ||
| Kernel.php | ||
| Request.php | ||