Move global admin controllers from Admin to SuperAdmin namespace

Backup, Update, Modules, and global Settings controllers (mail config,
PDF config, disk management, global settings) are application-wide features
not scoped to a company. Move them from Admin/ to SuperAdmin/ to match the
v3.0 UI structure where these live under Administration.

Company-scoped settings controllers remain in Admin/Settings/.

app/Http/Controllers/V1/SuperAdmin/Update/CheckVersionController.php

@@ -0,0 +1,35 @@
+<?php
+
+namespace App\Http\Controllers\V1\SuperAdmin\Update;
+
+use App\Http\Controllers\Controller;
+use App\Services\Update\Updater;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\File;
+
+class CheckVersionController extends Controller
+{
+    /**
+     * Handle the incoming request.
+     *
+     * @return JsonResponse
+     */
+    public function __invoke(Request $request)
+    {
+        if ((! $request->user()) || (! $request->user()->isOwner())) {
+            return response()->json([
+                'success' => false,
+                'message' => 'You are not allowed to update this app.',
+            ], 401);
+        }
+
+        set_time_limit(600); // 10 minutes
+
+        $channel = $request->get('channel', 'stable');
+        $version = preg_replace('~[\r\n]+~', '', File::get(base_path('version.md')));
+        $response = Updater::checkForUpdate($version, $channel);
+
+        return response()->json($response);
+    }
+}