Use CODEOWNERS instead of dependabot reviewers

[shenxianpeng]

Use CODEOWNERS instead of dependabot reviewers

Dependabot is now posting this comment as a warning:

The reviewers field in the dependabot.yml file will be removed soon. Please use the code owners file to specify reviewers for Dependabot PRs. For more information, see this blog post

Resolve that warning by replacing the reviewers entry in dependabot with a CODEOWNERS file.

Testing done

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue