Extend /process with info about available tasks and their types

[mikaelrss]

Description

We currently have no information about what available tasks exists for an app in the frontend. In the task: Altinn/app-frontend-react#1508 I am rewriting navigation to use the URL to contain the state about which task and which page the user is currently viewing. This gives the added benefit of being able to navigate to a particular page in a particular task.

To be able to do this we need to extend the current GET /process endpoint to contain information about all available tasks and their task types.

Additional Information

URL contains information about task and page:

Navigating to a previously closed task: