Expose project settings in REST API only for maintainer+ users

What does this MR do and why?

Expose project settings in REST API only for maintainer+ users

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

1. Add a user to as a Guest to a project.
2. Create a personal access token as that user and then query the REST API curl --header "Authorization: Bearer <ACCESS-TOKEN>" "http://127.0.0.1:3000/api/v4/projects/<PROJECT_ID>"
3. You shouldn't see any project settings.
4. However, if you upgraded that user to the Maintainer of the project, you should see all the project settings

Related to #442899 (closed)

ee/lib/ee/api/entities/project.rb

@@ -16,6 +16,14 @@ def preload_relation(projects_relation, options = {})
         end
 
         prepended do
+          with_options if: ->(project, options) { Ability.allowed?(options[:current_user], :read_issue, project) && project.feature_available?(:issuable_default_templates) } do
+            expose :issues_template
+          end
+
+          with_options if: ->(project, options) { Ability.allowed?(options[:current_user], :read_merge_request, project) && project.feature_available?(:issuable_default_templates) } do
+            expose :merge_requests_template
+          end
+
           with_options if: ->(project, options) { Ability.allowed?(options[:current_user], :admin_project, project) } do
             expose :approvals_before_merge, if: ->(project, _) { project.feature_available?(:merge_request_approvers) }
             expose :mirror, if: ->(project, _) { project.feature_available?(:repository_mirrors) }
@@ -29,6 +37,7 @@ def preload_relation(projects_relation, options = {})
             expose :marked_for_deletion_on, if: ->(project, _) { project.feature_available?(:adjourned_deletion_for_projects_and_groups) } do |project, _|
               project.marked_for_deletion_at
             end
+
             # Expose old field names with the new permissions methods to keep API compatible
             # TODO: remove in API v5, replaced by *_access_level
             expose :requirements_enabled do |project, options|
@@ -42,10 +51,6 @@ def preload_relation(projects_relation, options = {})
             expose :compliance_frameworks do |project, _|
               [project.compliance_framework_setting&.compliance_management_framework&.name].compact
             end
-            expose :issues_template, if: ->(project, options) do
-              project.feature_available?(:issuable_default_templates) &&
-                Ability.allowed?(options[:current_user], :read_issue, project)
-            end
 
             expose :merge_pipelines_enabled?, as: :merge_pipelines_enabled, if: ->(project, _) { project.feature_available?(:merge_pipelines) }
             expose :merge_trains_enabled?, as: :merge_trains_enabled, if: ->(project, _) { project.feature_available?(:merge_pipelines) }
@@ -56,11 +61,6 @@ def preload_relation(projects_relation, options = {})
 
             expose :restrict_pipeline_cancellation_role, as: :ci_restrict_pipeline_cancellation_role, if: ->(project, _) { project.ci_cancellation_restriction.feature_available? }
           end
-
-          expose :merge_requests_template, if: ->(project, options) do
-            project.feature_available?(:issuable_default_templates) &&
-              Ability.allowed?(options[:current_user], :read_merge_request, project)
-          end
         end
       end
     end