fix(external_api) add autoplay capabilities to created iframe

Should fix https://github.com/jitsi/jitsi-meet/issues/7037

modules/API/external/external_api.js

         const frameName = `jitsiConferenceFrame${id}`;
 
         this._frame = document.createElement('iframe');
-        this._frame.allow = 'camera; microphone; display-capture';
+        this._frame.allow = 'camera; microphone; display-capture; autoplay;';
         this._frame.src = this._url;
         this._frame.name = frameName;
         this._frame.id = frameName;