Support modifying startup variables for servers

app/Http/Requests/Api/Client/Servers/Startup/UpdateStartupVariableRequest.php

@@ -0,0 +1,30 @@
+<?php
+
+namespace Pterodactyl\Http\Requests\Api\Client\Servers\Startup;
+
+use Pterodactyl\Models\Permission;
+use Pterodactyl\Http\Requests\Api\Client\ClientApiRequest;
+
+class UpdateStartupVariableRequest extends ClientApiRequest
+{
+    /**
+     * @return string
+     */
+    public function permission()
+    {
+        return Permission::ACTION_STARTUP_UPDATE;
+    }
+
+    /**
+     * The actual validation of the variable's value will happen inside the controller.
+     *
+     * @return array|string[]
+     */
+    public function rules(): array
+    {
+        return [
+            'key' => 'required|string',
+            'value' => 'present|string',
+        ];
+    }
+}