Acceptance criteria

Given that I am allowed to organize events
When I generate an invitation list using Special:GenerateInvitationList
AND I enter an event page that is not in the event namespace
AND the selected namespace is in the list configured in community configuration (T387966)
Then the form submission will succeed

Given that I am allowed to organize events
When I generate an invitation list using Special:GenerateInvitationList
AND I enter an event page that is not in the event namespace
AND the selected namespace is NOT in the list configured in community configuration (T387966)
Then the event form submission will NOT be successful.
AND an error will be shown with the text: "{EventTitle} is not in a permitted namespace.".