Respect the default visibility level when creating a group

lib/api/groups.rb

@@ -7,7 +7,9 @@ module API
     helpers do
       params :optional_params_ce do
         optional :description, type: String, desc: 'The description of the group'
-        optional :visibility, type: String, values: Gitlab::VisibilityLevel.string_values, desc: 'The visibility of the group'
+        optional :visibility, type: String, values: Gitlab::VisibilityLevel.string_values,
+                 default: Gitlab::VisibilityLevel.string_level(Gitlab::CurrentSettings.current_application_settings.default_group_visibility),
+                 desc: 'The visibility of the group'
         optional :lfs_enabled, type: Boolean, desc: 'Enable/disable LFS for the projects in this group'
         optional :request_access_enabled, type: Boolean, desc: 'Allow users to request member access'
         optional :share_with_group_lock, type: Boolean, desc: 'Prevent sharing a project with another group within this group'

spec/requests/api/groups_spec.rb

@@ -444,6 +444,7 @@ describe API::Groups do
         expect(json_response["name"]).to eq(group[:name])
         expect(json_response["path"]).to eq(group[:path])
         expect(json_response["request_access_enabled"]).to eq(group[:request_access_enabled])
+        expect(json_response["visibility"]).to eq(Gitlab::VisibilityLevel.string_level(Gitlab::CurrentSettings.current_application_settings.default_group_visibility))
       end
 
       it "creates a nested group", :nested_groups do