Allow to change query string passthrough on a per-redirect basis (D8)

Assigning to myself as I'm triaging all RTBC issues.

Thanks for the issue, patches, testing, and review. The patch still applies cleanly and the option is added to the form. I didn't test it because...

I don't understand why this option is not a yes/no (true/false) option. What is default for?

This logic:

+      if ($redirect->getRedirectOption('passthrough_querystring') == 'always' || ($this->config->get('passthrough_querystring') && $redirect->getRedirectOption('passthrough_querystring') != 'never')) {

adds the $request_query if they choose always or if they didn't choose never which means they must have chosen default.

This seems overly complicated to me. Am I missing something? Moving to postponed for more explanation.

Agree on usability question in #13, but here's a patch for Drupal 10.5.x, redirect v1.12.