Allow CORS requests from localhost for development (#104385)

Allow CORS requests from `http://localhost:<port>`. Some webbrowsers
(like Safari) are picky about hostname vs. IP addresses, and this
makes them work well with the webapp development server.

Reviewed-on: https://projects.blender.org/studio/flamenco/pulls/104385
Reviewed-by: Sybren A. Stüvel <sybren@blender.org>

cmd/flamenco-manager/webservice.go

@@ -244,6 +244,7 @@ func corsOrigins(urls []url.URL) []string {
 		url.Host = fmt.Sprintf("%s:%d", url.Hostname(), developmentWebInterfacePort)
 		origins[i] = url.String()
 	}
+	origins = append(origins, fmt.Sprintf("http://localhost:%d", developmentWebInterfacePort))
 	log.Debug().Str("origins", strings.Join(origins, " ")).Msg("acceptable CORS origins")
 	return origins
 }