Add gitleaks config, exclude svgs

What does this MR do?

Add SVGs to the list of file exclusions. Include gitleaks.toml with default configuration plus SVG addition to regex.

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/10281

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