Possibility to download receipt (including form pdf)

For apps that are considered sensitive and thus does not save the submitted form data in Altinn after the form is completed, it would be a good feature for the users if they can send the initial receipt includning a pdf of the form to their email.
Then they can store the pdf in their own archive system.

This feature was requested by the Økokrim serviceowner for their new MT-3 app that is currently being developed in Altinn 3.

Start by reviewing how Altinn apps generate the initial receipt and form PDF, then trace the existing email-delivery flow. The issue provides no files, tests, or entry point, so first identify where receipt creation and email sending are implemented. Done means sensitive apps can send users an initial receipt containing the submitted form as a PDF for external archiving.

Written by the indexing model from the issue text.