Update incident fields

Future incident structure is about:
```
  assigned_to: <ID> (instead of assigned_fullname, assigned_user, assigned_user_id)
  freeze:
    state: true
    type: .... (prev. `frozen_until_source. + if no `frozen_until` set "inhibition")
    until: .... (prev. frozen_until)
  link ?
  version: v3.6.0
  uuid (removed)
```