Increase max size of passthroughs to 10MB

What does this MR do?

Increase file size maximum to accommodate larger rulesets. We have one example from gitlab-org/gitlab#423858 (closed) that is 1.2MB. This does not seem like a critical limitation.

What are the relevant issue numbers?

gitlab-org/gitlab#423858 (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