Support saving existing files

app/Http/Requests/Api/Client/Servers/Files/WriteFileContentRequest.php

@@ -0,0 +1,35 @@
+<?php
+
+namespace Pterodactyl\Http\Requests\Api\Client\Servers\Files;
+
+use Pterodactyl\Contracts\Http\ClientPermissionsRequest;
+use Pterodactyl\Http\Requests\Api\Client\ClientApiRequest;
+
+class WriteFileContentRequest extends ClientApiRequest implements ClientPermissionsRequest
+{
+    /**
+     * Returns the permissions string indicating which permission should be used to
+     * validate that the authenticated user has permission to perform this action aganist
+     * the given resource (server).
+     *
+     * @return string
+     */
+    public function permission(): string
+    {
+        return 'save-files';
+    }
+
+    /**
+     * There is no rule here for the file contents since we just use the body content
+     * on the request to set the file contents. If nothing is passed that is fine since
+     * it just means we want to set the file to be empty.
+     *
+     * @return array
+     */
+    public function rules(): array
+    {
+        return [
+            'file' => 'required|string',
+        ];
+    }
+}