Hello Nguyen, welcome to the world of Qlik. I know you will find it exciting.
Currently, no you cannot, Qlik Sense Cloud does not support extensions or images at the moment. You can request a trial of Qlik Sense Enterprise server though. You can contact our concierge service at Contact Qlik Qoncierge Service | Qlik - who can help and work with you.
Hi Javier - currently this is not possible - however we are working on certifying extensions to be used in the cloud. I don't have any more information on this yet - but will updated the community once I learn more.