Mailing outs

[jroneel]

Summary

Disabled the ability for users to add new "Mailing Outs" entries through both the main site and the crm section. The changes ensure that the "add" permission is removed for the "Mailing Outs" model in the CRM app.

Changes

Overrode the has_add_permission method in MailingOutAdmin to always return False, blocking users from adding Mailing Outs via the Django admin interface and hiding the "add" button in relevant admin views.
Updated tests to remove the "add" permission and "add" URL for the "Mailing Outs" model in the CRM app.

Pull Request Checklist

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