Build image from packaged release

What does this MR do?

Drop multi-stage docker image in favor of fetching gosec release

By no longer relying on the upstream securego image we can keep our base images up to date with a more regularly build cycle. This addresses vulnerabilities in upstream alpine images that securego/gosec image is currently vulnerable to

Extras

• Removes unnecessary setting of GO111MODULE since we are now on v1.13
• Adds proper error handling of gosec analyzer execution

What are the relevant issue numbers?

Relates to gitlab-org/gitlab#215078 (closed)

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
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer