Update CODEOWNERS

[tylerrinnan-wf]

Which problem is this PR solving?

CODEOWNERS does not reflect accurate maintainers for opentelemetry-dart.

Short description of the change

Update CODEOWNERS to include @blakeroberts-wk as primary maintainer of the opentelemetry-dart project in place of @Workiva/observability

How Has This Been Tested?

No tests required

Checklist:

• [ ] Unit tests have been added
• [ ] Documentation has been updated

[aviary3-wk]

Security Insights

No security relevant content was detected by automated scans.

Action Items

• Review PR for security impact; comment "security review required" if needed or unsure

• Verify aviary.yaml coverage of security relevant code

  Questions or Comments? Reach out on Slack: #support-infosec.

[kennytrytek-wf]

@Workiva/release-management-pp

[blakeroberts-wk]

QA +1 documentation only