ApiWrapper dirty flag handling

Vorschlag:
```js
this.dirty = this.dirty || this.localValue !== this.apiValue
```

_Originally posted by @pmattmann in https://github.com/ecamp/ecamp3/pull/2572#discussion_r848768966_

1. Specify how ApiWrapper should handle beeing dirty
- Proposal by @usu: similar behaviour like the drag and drop of contentnodes and waiting for the last request
2. Adapt the tests (maybe refactoring) that they reflect the specification
3. Implement the behaviour specified in the tests
4. Test in the frontend that the specified behaviour matches the needs of the users
5. Maybe adapt the tests
6. Implement
7. Repeat from 4