feat: vcard services for import/export (#1996)

Improve CardDAV with write functions

app/Http/Controllers/CardDAV/SapiServerMock.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace App\Http\Controllers\CardDAV;
+
+use Sabre\HTTP\Sapi;
+use Sabre\HTTP\ResponseInterface;
+
+/**
+ * Mock version of SapiServer to avoid 'header()' calls.
+ */
+class SapiServerMock extends Sapi
+{
+    public static function sendResponse(ResponseInterface $response)
+    {
+    }
+}