Merge branch 'ag-restore-convdev-docs-page-with-rename-info' into 'master'

Restore ConDev docs page with a redirect to new docs

See merge request gitlab-org/gitlab!23954

doc/user/admin_area/monitoring/convdev.md

+---
+redirect_to: '../../instance_statistics/dev_ops_score.md'
+---
+
+Conversational Development Index was renamed to [DevOps Score](../../instance_statistics/dev_ops_score.md) in GitLab 12.6.