Add a validator Ruby class to validate CODEOWNERS

• Define different cases of errors and warnings for Codeowner file based on Document CODEOWNER syntax and logic (&10057 - closed) • Unassigned
• Create a validator class that surfaces these errors and warnings
• Potentially also start tracking broken files. If not then follow up with Iteration 1: Implement metrics to measure the n... (#389564 - closed)

Potentially use this function as a basis: #219916 (comment 1311635444)