Introduce SAST.latest and Secret-Detection.latest CI templates

Proposal

We already have a SAST-IaC.latest.gitlab-ci.yml template. We should consider introducing Category:SAST and Category:Secret Detection templates as well. These provide us safer ways of rolling out new changes to our templates to a subset of opted-in users with potential for breaking changes.

• latest template guidelines https://docs.gitlab.com/ee/development/cicd/templates.html#latest-version