nextcloud: create admin user via occ

nixpkgs removed services.nextcloud.config.{adminuser,adminpassFile} and
now installs with --disable-admin-user. Add a nextcloud-admin-user oneshot
that creates the admin account from the vars secret after nextcloud-setup.

modules/clan/nextcloud/default.nix

@@ -42,10 +42,27 @@
             dbhost = lib.mkDefault "/run/postgresql";
             dbuser = lib.mkDefault "nextcloud";
             dbname = lib.mkDefault "nextcloud";
-            adminuser = lib.mkDefault "admin";
-            adminpassFile = lib.mkDefault config.clan.core.vars.generators.nextcloud.files.adminpassFile.path;
           };
+        };
 
+        # nixpkgs installs Nextcloud with --disable-admin-user; create the
+        # admin account ourselves once the instance is installed.
+        systemd.services.nextcloud-admin-user = {
+          wantedBy = [ "multi-user.target" ];
+          after = [ "nextcloud-setup.service" ];
+          requires = [ "nextcloud-setup.service" ];
+          before = [ "phpfpm-nextcloud.service" ];
+          path = [ config.services.nextcloud.occ ];
+          serviceConfig = {
+            Type = "oneshot";
+            User = "nextcloud";
+          };
+          script = ''
+            if ! nextcloud-occ user:info admin >/dev/null 2>&1; then
+              NC_PASS="$(<${config.clan.core.vars.generators.nextcloud.files.adminpassFile.path})" \
+                nextcloud-occ user:add admin --password-from-env --group admin
+            fi
+          '';
         };
 
         clan.core.state.nextcloud.folders = [