Add error.html for caddy

containers/nextcloud/collaboraoffice.caddy

@@ -1,4 +1,6 @@
 office.[DOMAIN] {
+	import gateway_error
+
 	@browser path /browser*
 	reverse_proxy @browser collaboraoffice:9980
 

containers/nextcloud/nextcloud.caddy

@@ -1,4 +1,6 @@
 cloud.[DOMAIN] {
+	import gateway_error
+
 	# Warning HSTS Nextcloud
 	header Strict-Transport-Security "max-age=15552000; includeSubDomains"