Suggesting code owners as approvers does not work in Starter

Steps to reproduce

1. Add Starter license to the GitLab instance.
2. Create project and set up CODEOWNERS file inside (e.g. assign a user to be code owner of all of the files in the project).
3. Start creating merge request.

Relevant logs and/or screenshots

In Omnibus test instance with Ultimate license everything works as expected, related rails output:

$ sudo gitlab-rails console
-------------------------------------------------------------------------------------
 GitLab:       11.4.3-ee (dce6f33d651)
 GitLab Shell: 8.3.3
 postgresql:   9.6.8
-------------------------------------------------------------------------------------
Loading production environment (Rails 4.2.10)
irb(main):001:0> License.first.plan
=> "ultimate"
irb(main):002:0> License.current.feature_available?(:code_owners)
=> true
irb(main):003:0> License.current.feature_available?(:code_owner_as_approver_suggestion)
=> true

Same output in Docker test instance with Starter license:

# docker exec -it gitlab gitlab-rails console
-------------------------------------------------------------------------------------
 GitLab:       11.4.3-ee (dce6f33)
 GitLab Shell: 8.3.3
 postgresql:   9.6.8
-------------------------------------------------------------------------------------
Loading production environment (Rails 4.2.10)
irb(main):001:0> License.first.plan
=> "starter"
irb(main):002:0> License.current.feature_available?(:code_owners)
=> true
irb(main):003:0> License.current.feature_available?(:code_owner_as_approver_suggestion)
=> false