`anonymous_searches_allowed` setting is not supported yet
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/189902
## Implementation Guide
- Add `AnonymousSearchesAllowed` to the [Settings struct](https://gitlab.com/gitlab-org/api/client-go/-/blob/main/settings.go#L54)
- Add `AnonymousSearchesAllowed` to the [UpdateSettingsOptions struct](https://gitlab.com/gitlab-org/api/client-go/-/blob/main/settings.go#L542)
- Update or add a new test to [settings_test.go](https://gitlab.com/gitlab-org/api/client-go/-/blob/main/settings_test.go) which includes setting this value.
issue