Flag for showing hidden field in summary

### Description

Sometimes we need to show a computed value/label for a field in the summary page instead of its data model value. The computed field can be implemented as a hidden field, but then it will not show in the summary page.

It should be possible to set a flag in the layout file so that a hidden field is shown in the summary page. This should work also for groups so it needs to be set in the page layout.

Something like this:
```
{
"id": "someComputedFieldWhichMayBePartOfAGroup",
"type": "Input",
"textResourceBindings": {
"title": "Title"
},
"dataModelBindings": {
"simpleBinding": "ComputedField"
},
"hidden": true,
"showInSummary": true
}
```

### Additional Information

- https://altinn.slack.com/archives/C03DX42K6AY/p1678722640148919