archweb: Redirect /pacman/ to new pacman subdomain[1]

[1] c55b448c ("Add GitLab Pages for pacman")

roles/archweb/templates/nginx.d.conf.j2

@@ -144,8 +144,8 @@ server {
         alias {{ archweb_dir }}/collected_static/favicon.ico;
     }
 
-    location /pacman/ {
-        alias {{ archweb_dir }}/archlinux.org/pacman/;
+    location ~ ^/pacman/(.*)$ {
+        return 301 https://pacman.archlinux.page/$1;
     }
 
     location /netcfg/ {