Add flag to control bundler-audit self-updates

What does this MR do?

This MR does the following:

• adds an env flag to allow user control of whether or not bundler audit self-updates
• runs bundler audit update as part of the docker build step

What are the relevant issue numbers?

gitlab-org/gitlab#33718 (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