SAST documentation: latest template is referenced in docs
### Documentation :chart_with_upwards_trend:
Our documentation does not include information about the [latest template](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/ci/templates/Jobs/SAST.latest.gitlab-ci.yml).
This template has features that are unavailable in the regular template (specifically, MR pipeline support).
Add a heading to the [SAST docs page](https://docs.gitlab.com/ee/user/application_security/sast/) that covers the current offering available with the `latest` template, while clarifying that it is less stable.
#### Success Criteria
- [x] Submit a documentation update MR
- [x] Pass ~"group::static analysis" review
- [x] Pass ~"Technical Writing" review
- [x] Merge the update
- [x] Update ~"group::static analysis" [OKR](https://gitlab.com/gitlab-com/gitlab-OKRs/-/work_items/8107)
issue