Send notifications about login with new client or country (#4032)

* Send notifications about login with new client or country

* Rebase migration

* Remove immediately

* Fix isort

* Text update

src/pretix/control/logdisplay.py

@@ -455,6 +455,8 @@ def pretixcontrol_logentry_display(sender: Event, logentry: LogEntry, **kwargs):
         'pretix.event.export.schedule.executed': _('A scheduled export has been executed.'),
         'pretix.event.export.schedule.failed': _('A scheduled export has failed: {reason}.'),
         'pretix.control.auth.user.created': _('The user has been created.'),
+        'pretix.control.auth.user.new_source': _('A first login using {agent_type} on {os_type} from {country} has '
+                                                 'been detected.'),
         'pretix.user.settings.2fa.enabled': _('Two-factor authentication has been enabled.'),
         'pretix.user.settings.2fa.disabled': _('Two-factor authentication has been disabled.'),
         'pretix.user.settings.2fa.regenemergency': _('Your two-factor emergency codes have been regenerated.'),