Use `.latest` templates to stage breaking changes in vendored templates and analyzers

Release notes

Problem to solve

As an engineer, I want a mechanism to release new and changed functionality without worrying about backwards compatibility. Not having this capability adds significant work when preparing for and executing tasks which are part of major releases.

Proposal

Feature flags are used in the rails platform and GitLab FE to stage changes, providing a nice and progressive rollout strategy. We lack this ability in Sec analyzers, particularly as it relates to vendored CI templates and the analyzers themselves. There is a roughly equivalent paradigm in vendored templates which we might be able to take better advantage of: https://docs.gitlab.com/ee/development/cicd/templates.html#latest-version. Utilizing these templates throughout the section could significantly reduce complexity in producing and releasing breaking changes in the analyzers themselves.

Intended users

Feature Usage Metrics