Move Security vendored templates into the Jobs subdir

Summary

With the recent changes of Composable AutoDevops, a new directory call Jobs has been created for the purpose of per job templates that needs to be used with the include feature.

This is exactly what our Security vendored template are for so we should make this consistent.

Proposal

• Make sure we never advertise on using the Security prefix when using the vendored security templates
• Move templates to the Jobs subdir

NB: as a side effect of this change, the vendored template won't be discoverable anymore as they won't be listed in the template dropdown in Gitlab UI. Providing a way to discover and include job templates via the UI is being addressed in #job in https://gitlab.com/gitlab-org/gitlab-ce/issues/53307