Add craigmsmith as codeowner and maintainer

What does this MR do?

Add @craigmsmith as a CODEOWNER

The ruleset project currently has only one active maintainer. To alleviate pressure from @theoretick and replenish the maintainer pool, this MR adds me @craigmsmith as a CODEOWNER, and if accepted @craigmsmith permissions should be updated to maintainer

I have several contributions to this repo and since SAST is the biggest user of the ruleset project I feel I am in a good position to maintain this project.

Contributes

• Extend ProcessPassthrough testing (!37 - merged) • Craig Smith • 17.2
• Fix: do not update file passthrough value for l... (!34 - merged) • Craig Smith • 17.2
• [Refactor] Replace reflect with require in unit... (!42 - merged) • Craig Smith • 17.2

Reviews

• Update dependency go-git to v5.11.0 (!25 - merged) • Jason Leasure • 16.10
• Increase max size of passthroughs to 10MB (!24 - merged) • Connor Gilbert • 16.4
• Fix incorrect reference to Remote Custom rulese... (!23 - merged) • Vishwa Bhat • 16.4
• chore: Fix typo in passthrough logging (!12 - merged) • Lucas Charles • 15.11

What are the relevant issue numbers?

NA

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