Fetch FrontEndSettings section from appSettings when this file is fetched with react query

[standeren]

Description

We need to implement endpoint to fetch the appsettings file, or maybe only the specific section needed?

Expressions need the frontendsettings section from appsettings file, which is the app-specific configs entered by app-developers.

This implementation is therefor put on hold.

Related Issues

• #10501
• #10727

### Tasks
- [ ] https://github.com/Altinn/altinn-studio/issues/11237
- [ ] Populate frontendSettings object in expressions with values from FrontEndSettings object from appSettings

Considerations

Should we serve Studio with the union of all values from this section from all the environments-settings-files or only one of them and assume all the values are present in all files? In that case which? Or should we visualize what environment the value is connected to or let the user first select which env to see the values from?

[nkylstad]

@standeren Is this still something we need?