The $wgEnableImageWhitelist configuration option permits allowing non-local images if they match an allow list.
This is not used in production at WMF, and it's not clear that Parsoid will support this functionality (T75581). But the name is also problematic, and is used in a bunch of related code.
If we're going to go through the trouble of deprecating this configuration and the various functions which reference it, it's possible we should just do T254802: Make the external image block list / allow list into an extension instead.