Use `duo_features_enabled` setting

* Can be set on a project to block code suggestions
* Later on, we will use the same setting name to block duo chat and other
  features on projects. We will also use the same setting for groups and
  subgroups.
* This will not take effect until we enable the
  `purchase_code_suggestions` feature flag because until then the group
  setting for `code_suggestions` + Ultimate license enableds access.
* After whereas after that flag is enabled, access will be determined by
  whether the user has a licensed seat. See
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/138334
* https://gitlab.com/groups/gitlab-org/-/epics/12404#note_1748487091