D8 - Config form not saving unoconv url

If you enter a API url it doesn't seem to be saved in the form.

It looks like UnoconvConfigForm is using a mix of config and settings (looking for settings, saving config).

I guess you just need to figure out what's best, config or settings?

If using config, it's probably best practice to use the current Core based approach (see Drupal\system\Form\SiteInformationForm), and then use a settings.php override of the $config variable if you need to.

Even though there is an annoyance with settings.php based overrides...
(https://www.drupal.org/project/drupal/issues/2408549)