DOP-4669: follow up - add custom env var to sls (#1048)

add custom env var to sls

Author: seungpark

infrastructure/ecs-main/serverless.yml

@@ -107,6 +107,7 @@ custom:
   gatsbyTestEmbedVersions: ${ssm:/env/${self:provider.stage}/docs/worker_pool/flag/embedded_versions}
   gatsbyHideUnifiedFooterLocale: ${ssm:/env/${self:provider.stage}/docs/worker_pool/flag/hide_locale}
   gatsbyMarianURL: ${ssm:/env/${self:provider.stage}/docs/worker_pool/frontend/marian_url}
+  gatsbyEnableDarkMode: ${ssm:/env/${self:provider.stage}/docs/worker_pool/frontend/enable_dark_mode}
   fastlyMainToken: ${ssm:/env/${self:provider.stage}/docs/worker_pool/fastly/docs/main/token}
   fastlyMainServiceId: ${ssm:/env/${self:provider.stage}/docs/worker_pool/fastly/docs/main/service_id}
   fastlyCloudManagerToken: ${ssm:/env/${self:provider.stage}/docs/worker_pool/fastly/docs/cloudmanager/token}