Make the config translatable

I have opened a new MR here https://git.drupalcode.org/project/commerce_ajax_atc/-/merge_requests/4, the patch works on our website.

Forgot to update the status ):

Note: For us, the regular text field was too short as we needed to add a link & markup in the message. For that to also work with translations, we had to change the type from label to text on top of that, so that config translation displays it as a textarea.

Let us know if we should include that in the MR.

Thanks for the work on this. I'm flexible here @bedir.

Feel free to add that to the merge request.