Allow uploads of webp and jpeg xl image formats

The web platform continues to evolve, and new image formats have cropped up, offering clearer pictures in smaller file sizes. We should allow newer formats such as webp an jpeg xl to be uploaded anywhere images can be uploaded.

While this may not make much of a difference to the average user, it may be especially useful for any designers who are uploading assets to Aha!, as their software is most likely able to export these formats.