Default enable FF group_level_vulnerability_report_grouping

Changelog: changed

config/feature_flags/development/group_level_vulnerability_report_grouping.yml

@@ -5,4 +5,4 @@ rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/432778
 milestone: '16.7'
 type: development
 group: group::threat insights
-default_enabled: false
+default_enabled: true