Show the total number of attachments under “Vedlegg” even if they are grouped on the receipt page

### Description

If you have uploaded attachments in your form and divided them into separate groups for the receipt page, “Vedlegg” will still show 0.

Wouldn't it be a good idea to have all groups as subheadings under “Vedlegg” that show the total number of attachments instead?

Example of attachments with 0, and a subheading of a group from `applicationmetadata.json`:

### Additional Information

_No response_

Start by tracing the receipt-page rendering for “Vedlegg” and how attachment groups from applicationmetadata.json are read. Confirm the current zero count when attachments are grouped, then verify that the receipt shows each group as a subheading and the total attachment count.

Written by the indexing model from the issue text.