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/Services/PDFDrivers/GotenbergPDFDriver.php

@@ -0,0 +1,59 @@
+<?php
+
+namespace App\Services\PDFDrivers;
+
+use Gotenberg\Gotenberg;
+use Gotenberg\Stream;
+use Illuminate\Http\Response;
+
+class GotenbergPDFResponse
+{
+    /** @var \Psr\Http\Message\ResponseInterface */
+    protected $response;
+
+    public function __construct($stream)
+    {
+        $this->response = $stream;
+    }
+
+    public function stream(string $filename = 'document.pdf'): Response
+    {
+        $output = $this->response->getBody();
+
+        return new Response($output, 200, [
+            'Content-Type' => 'application/pdf',
+            'Content-Disposition' => 'inline; filename="'.$filename.'"',
+        ]);
+    }
+
+    public function output(): string
+    {
+        return $this->response->getBody()->getContents();
+    }
+}
+
+class GotenbergPDFDriver
+{
+    public function loadView(string $viewname): GotenbergPDFResponse
+    {
+        $papersize = explode(' ', config('pdf.gotenberg.papersize'));
+        if (count($papersize) != 2) {
+            throw new \InvalidArgumentException('Invalid Gotenberg Papersize specified');
+        }
+
+        $host = config('pdf.gotenberg.host');
+        $request = Gotenberg::chromium($host)
+            ->pdf()
+            ->margins(0, 0, 0, 0) // Margins can be set using CSS
+            ->paperSize($papersize[0], $papersize[1])
+            ->html(
+                Stream::string(
+                    'document.html',
+                    view($viewname)->render(),
+                )
+            );
+        $result = Gotenberg::send($request);
+
+        return new GotenbergPDFResponse($result);
+    }
+}