fix(backport): Add missing sample config

Signed-off-by: Joas Schilling <coding@schilljs.com>

config/config.sample.php

@@ -303,6 +303,15 @@ $CONFIG = [
  */
 'auth.bruteforce.protection.enabled' => true,
 
+/**
+ * Whether the rate limit protection shipped with Nextcloud should be enabled or not.
+ *
+ * Disabling this is discouraged for security reasons.
+ *
+ * Defaults to ``true``
+ */
+'ratelimit.protection.enabled' => true,
+
 /**
  * Whether the authtoken v1 provider should be skipped
  *