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

config/pdf.php

@@ -0,0 +1,14 @@
+<?php
+
+return [
+
+    'driver' => env('PDF_DRIVER', 'gotenberg'),
+
+    'gotenberg' => [
+        'host' => env('GOTENBERG_HOST', 'http://pdf:3000'),
+        'papersize' => env('GOTENBERG_PAPERSIZE', '210mm 297mm'),
+    ],
+
+    'dompdf' => [],
+
+];