✨(domains) add action required status on MailDomain

Create a new domain status to handle cases where
action is required from an external domain owner
for a domain to be fully functional.

src/backend/mailbox_manager/enums.py

@@ -22,6 +22,7 @@ class MailDomainStatusChoices(models.TextChoices):
     ENABLED = "enabled", _("Enabled")
     FAILED = "failed", _("Failed")
     DISABLED = "disabled", _("Disabled")
+    ACTION_REQUIRED = "action_required", _("Action required")
 
 
 class MailboxStatusChoices(models.TextChoices):