Support webp files

[LosHawlos]

Hi,

I tried to warp the following map:
https://commons.wikimedia.org/wiki/File:Gemarkung_Mannheim_mit_Umgebung_LABW_Generallandesarchiv_Karlsruhe_H_Mannheim_104_detail_1911.webp

It fail with the error:

Add new map from Wikimedia Commons
Invalid Fields
Correct the following errors and try again.

Upload content type is invalid
Upload is invalid

I think this might be caused by the file being in webp format. Could this be supported?

Thanks!