Backport API::Helpers::ProjectsHelpers from EE

This backports all changes made to this module in EE to CE, and wraps EE
specific code in a conditional.

lib/api/helpers/projects_helpers.rb

@@ -31,17 +31,19 @@ module API
             optional :initialize_with_readme, type: Boolean, desc: "Initialize a project with a README.md"
           end
 
-          params :optional_project_params_ee do
-            optional :repository_storage, type: String, desc: 'Which storage shard the repository is on. Available only to admins'
-            optional :approvals_before_merge, type: Integer, desc: 'How many approvers should approve merge request by default'
-            optional :external_authorization_classification_label, type: String, desc: 'The classification label for the project'
-            optional :mirror, type: Boolean, desc: 'Enables pull mirroring in a project'
-            optional :mirror_trigger_builds, type: Boolean, desc: 'Pull mirroring triggers builds'
+          if Gitlab.ee?
+            params :optional_project_params_ee do
+              optional :repository_storage, type: String, desc: 'Which storage shard the repository is on. Available only to admins'
+              optional :approvals_before_merge, type: Integer, desc: 'How many approvers should approve merge request by default'
+              optional :external_authorization_classification_label, type: String, desc: 'The classification label for the project'
+              optional :mirror, type: Boolean, desc: 'Enables pull mirroring in a project'
+              optional :mirror_trigger_builds, type: Boolean, desc: 'Pull mirroring triggers builds'
+            end
           end
 
           params :optional_project_params do
             use :optional_project_params_ce
-            use :optional_project_params_ee
+            use :optional_project_params_ee if Gitlab.ee?
           end
         end
       end