Make ci_secrets_syntax flag disabled by default

and extract check in Gitlab::Ci::Features.

ee/lib/ee/gitlab/ci/config/entry/job.rb

@@ -27,7 +27,7 @@ module EE
             end
 
             def secrets_enabled?
-              ::Feature.enabled?(:ci_secrets_syntax, default_enabled: true)
+              ::Gitlab::Ci::Features.secrets_syntax_enabled?
             end
           end
         end

ee/lib/ee/gitlab/ci/features.rb

+# frozen_string_literal: true
+
+module EE
+  module Gitlab
+    module Ci
+      module Features
+        extend ActiveSupport::Concern
+
+        prepended do
+          def self.secrets_syntax_enabled?
+            ::Feature.enabled?(:ci_secrets_syntax)
+          end
+        end
+      end
+    end
+  end
+end

lib/gitlab/ci/features.rb

@@ -44,3 +44,5 @@ module Gitlab
     end
   end
 end
+
+::Gitlab::Ci::Features.prepend_if_ee('::EE::Gitlab::Ci::Features')