Include instance owner party information in all APIs returning instance information

### Description

As of https://github.com/Altinn/app-lib-dotnet/pull/1229

We return instance owner party information (such as name) along with the rest of the instance information for the POST and GET (by instance ID) API endpoints, but not any others (se non-exhaustive list in linked PR).

It would be less surprising if the party information was added to all the places where we return the `Instance` today. This would mean we always return `InstanceResponse` and never `Instance`.

A counter argument would be that this information never changes, so it makes less sense to include as part of mutating operation responses such as data patching and user actions, but might still be worthwhile due to the potential surprise (there used to be only 1 variant).

### Additional Information

_No response_

### Tasks

_No response_

### Acceptance Criterias

- [ ] `Instance` is no longer part of OpenAPI schema, we always return `InstanceResponse` in its' place

Start by reviewing PR #1229 and the non-exhaustive list of APIs that return Instance, then inspect the generated or declared OpenAPI schema. Update the affected responses so InstanceResponse is used everywhere instance information is returned, and confirm that Instance no longer appears in the OpenAPI schema.

Written by the indexing model from the issue text.