luci-proto-wireguard: grant uci read access to system and ddns config

The configuration export requires access to /e/c/system and /e/c/ddns for
external hostname hints.

Fixes: #5838
Fixes: 9ba20645b0 ("luci-proto-wireguard: rewrite protocol handler")
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

protocols/luci-proto-wireguard/root/usr/share/rpcd/acl.d/luci-wireguard.json

@@ -4,7 +4,8 @@
 		"read": {
 			"file": {
 				"/usr/bin/qrencode --inline --8bit --type=SVG --output=- -- *": [ "exec" ]
-			}
+			},
+			"uci": [ "ddns", "system" ]
 		},
 		"write": {
 			"ubus": {