WIP: Trigger sast-benchmark pipelines for new tags

What does this MR do?

This MR adds a new post stage to .gitlab-ci.yml to trigger a new pipeline in the sast-benchmark project for all new tags in this project.

An example pipeline for this branch that triggered the sast-benchmark pipeline: https://gitlab.com/gitlab-org/security-products/sast/pipelines/130174792 (.gitlab-ci.yml has since been changed to only trigger sast-benchmark on tags)

What are the relevant issue numbers?

closes sast-benchmark#11

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Job definition example
  • CI Templates (to be removed)
  • Vendored CI Templates (also in CE)
  • Ensure that all of the ENV vars supported are propagated to Docker containers upon docker run in job definitions
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer