feat(backups): use parallel gzip for volume backups

Add pigz to the helper image, select it when available with gzip fallback, and log the selected compressor in development.

config/constants.php

@@ -3,7 +3,7 @@
 return [
     'coolify' => [
         'version' => env('COOLIFY_VERSION') ?: '4.3.3',
-        'helper_version' => '1.0.14',
+        'helper_version' => '1.0.15',
         'realtime_version' => '1.0.17',
         'railpack_version' => '0.23.0',
         'self_hosted' => env('SELF_HOSTED', true),