[WIP] Add API endpoint for :remove_log service

Currently the specs do not pass.
```
  Failure/Error: response = patch "/jobs/#{job.id}/log", { reason: 'Because reason!' }, headers
  NoMethodError:
    undefined method `permission?' for nil:NilClass
```

Not entirely clear to me how `current_uesr` is `nil` for `RemoveLog`
service and not for a similarly (but critically differently) set up
`CancelJob` service.