[feature] Allow to upload multiple images to an event

Hi, It would be great to be able to have more than one image for an event. Currently, it is only possible to add additional images through the fediverse which is very limited and not so intuitive for most of the people that uses gancio. If this were possible would be nice to be able to choose which one is the cover and the rest could appear on the event page just smaller, so you know you can click on them to see them better but they are not too annoying and taking too much space on the screen (imagining the case of more than one additional image). Thank you!