Feat(Gotenberg): Opt-in alternative pdf generation for modern CSS (#184)

* WIP(gotenberg): add pdf generation abstraction and UI

* feat(pdf): settings validate(clien+server) & save

* fix(gotenberg): Use correct default papersize
chore(gotengberg): Remove unused GOTENBERG_MARGINS env from .env

* style(gotenberg): fix linter/styling issues

* fix(pdf): use pdf config policy

* fix: revert accidental capitalization in mail config vue

* Update composer, remove whitespace typo

* Fix small typos

* fix cookie/env issue

* Add gotenberg to .dev, move admin menu item up

app/Http/Controllers/V1/Admin/Settings/PDFConfigurationController.php

@@ -0,0 +1,54 @@
+<?php
+
+namespace App\Http\Controllers\V1\Admin\Settings;
+
+use App\Http\Controllers\Controller;
+use App\Http\Requests\PDFConfigurationRequest;
+use App\Space\EnvironmentManager;
+
+class PDFConfigurationController extends Controller
+{
+    /**
+     * @var EnvironmentManager
+     */
+    protected $environmentManager;
+
+    public function __construct(EnvironmentManager $environmentManager)
+    {
+        $this->environmentManager = $environmentManager;
+    }
+
+    public function getDrivers()
+    {
+        $this->authorize('manage pdf config');
+
+        $drivers = [
+            'dompdf',
+            'gotenberg',
+        ];
+
+        return response()->json($drivers);
+    }
+
+    public function getEnvironment()
+    {
+        $this->authorize('manage pdf config');
+
+        $config = [
+            'pdf_driver' => config('pdf.driver'),
+            'gotenberg_host' => config('pdf.gotenberg.host'),
+            'gotenberg_margins' => config('pdf.gotenberg.margins'),
+            'gotenberg_papersize' => config('pdf.gotenberg.papersize'),
+        ];
+
+        return response()->json($config);
+    }
+
+    public function saveEnvironment(PDFConfigurationRequest $request)
+    {
+        $this->authorize('manage pdf config');
+        $results = $this->environmentManager->savePDFVariables($request);
+
+        return response()->json($results);
+    }
+}