Enable :disable_service_templates FF by default

This effectively disables service templates, but gives
users the ability to re-enable them by
disabling the feature flag.

Changelog: changed

config/feature_flags/development/disable_service_templates.yml

@@ -5,4 +5,4 @@ rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/327436
 milestone: '13.12'
 type: development
 group: group::ecosystem
-default_enabled: false
+default_enabled: true