Add Thumbnail Support to the File Upload Component

### Description

**Thumbnail Support in File Upload Component**
Patentstyret would like to add thumbnail support to the FileUpload component. We have created an initial implementation that provides the necessary foundation for displaying images or thumbnails within the component.
The current implementation focuses on the infrastructure required to support thumbnails. Thumbnail generation itself is not included and must be implemented by the TE. This is due to a combination of factors:
* Licensing considerations related to available NuGet packages, where some suitable alternatives are not open source.
* The need to align the implementation with the latest updates and architectural changes in the codebase.

**Related PRs**
Frontend: https://github.com/Altinn/app-frontend-react/pull/3898
Backend: https://github.com/Altinn/app-lib-dotnet/pull/1598
Storage: https://github.com/Altinn/altinn-storage/pull/883 (merged)
App Local Test: https://github.com/Altinn/app-localtest/pull/183
Documentation: https://github.com/Altinn/altinn-studio-docs/pull/2602

**Further Information About the Implementation**
* Frontend - The frontend PR includes visual mockups/sketches demonstrating how thumbnails should be presented in the FileUpload component.
* Documentation - The documentation PR contains example code and implementation guidance for app developers who want to make use of the current thumbnail functionality.

**Known Areas for Improvement**
* Refactor and improve parts of the frontend implementation.
* Consider replacing the current hardcoded thumbnail data type ID with a configurable property on dataTypes.
* Improve backend caching and cache handling for thumbnail.

### Additional Information

I have updated @ivarne and @framitdavid about this issue and the work completed so far. They will take over and continue working towards the final solution.

Start with the frontend implementation and visual mockups in PR 3898, then review the FileUpload component against the listed improvement areas: frontend refactoring, configurable thumbnail data type IDs, and caching coordination. The issue does not define a final acceptance condition; confirm the remaining scope with the people taking over the work.

Written by the indexing model from the issue text.