Update Gitleaks and SD Rules version

What does this MR do?

• Update Gitleaks version to v8.28.0
• Update SD Rules version to v0.13.0 | gitlab-org/security-products/secret-detection/secret-detection-rules!142 (merged)
  • Fixes rule Alibaba AccessKey ID to report fewer FPs
  • Includes .git directory in the allowlists to fix the bug reported in v7.10.0
  • Includes low-risk files and directories in the allowlists to skip them during the scan
• Adds integration test to confirm allowlists behaviour

NOTE: I chose the pessimistic approach of verifying every pattern defined in the allowlist patterns by creating a dedicated file/directory (hence ~70 changes) and expecting analyzer to exclude it in the integration test.

What are the relevant issue numbers?

gitlab-org/gitlab#560147 (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 updated/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