12446 add datamodel to process tasklayoutset

[standeren]

Description

When data task have no data type:

When selecting data type:

After selecting:

If selecting a task that have no connected layoutset yet, the data type selector will not be visible:

https://github.com/Altinn/altinn-studio/assets/71079896/891e7787-a478-455e-87bf-c54385d85496

This PR uses the event setup in backend

Related Issue(s)

• #{issue number}

Verification

• [x] Your code builds clean without any errors or warnings
• [x] Manual testing done (required)
• [x] Relevant automated test added (if you find this hard, leave it and we'll help out)

Documentation

• [ ] User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)