- user can add an externally created mail domain
from UI and see the mail domain status on mail
domain page and left panel links.
- user can not create mailboxes to domain if mail
domain status is not equal to `enabled`
- update related tests and translations
Used https://github.com/openfun/joanie as boilerplate, ran a few
transformations with ChapGPT and adapted models and endpoints to
fit to my current vision of the project.
