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/Settings/GetSettingsController.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace App\Http\Controllers\V1\SuperAdmin\Settings;
+
+use App\Http\Controllers\Controller;
+use App\Http\Requests\GetSettingRequest;
+use App\Models\Setting;
+use Illuminate\Http\Request;
+use Illuminate\Http\Response;
+
+class GetSettingsController extends Controller
+{
+    /**
+     * Handle the incoming request.
+     *
+     * @param  Request  $request
+     * @return Response
+     */
+    public function __invoke(GetSettingRequest $request)
+    {
+        $this->authorize('manage settings');
+
+        $setting = Setting::getSetting($request->key);
+
+        return response()->json([
+            $request->key => $setting,
+        ]);
+    }
+}