Add registry event info to metadata tools

What does this MR do?

1. Resolve env variable REGISTRY_TRIGGERED in Environment.
2. Set the following to metadata.tools to sbom converter.
   1. { "vendor": "gitlab", "name": "container_registry" }

Steps to test

1. Set newly introduced env variable.
2. Run the CS.
3. Verify that the SBOM report has newly introduced instigator identifier.

Screenshot

What are the relevant issue numbers?

gitlab-org/gitlab#443631 (closed)

Does this MR meet the acceptance criteria?

• Changelog trailer 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