add controller for handling generic events

[chrrust]

Description

The purpose of this PR is to synchronize the endpoints for events between Altinn Platform and localtest. In Altinn Events API, there are two endpoints for processing events. One for app events, and one for generic events. Currently, only the app events endpoint is present in localtest.

The PR adds an endpoint for processing generic events. Validation works the same as in Altinn Events API. However, as with app events, the events are just saved to a file and not done anything with.

The added endpoint for generic events is the same as the app events endpoint with some minor tweaks for validation and routing.

Verification

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

[chrrust]

@ivarne Har du mulighet til å merge? Har ikke rettigheter til det