GraphQL node for CODEOWNER file validator

What does this MR do and why?

GraphQL node for CODEOWNER file validator

Changelog: added EE: true

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. create a CODEOWNERS file with errors
2. call GQL query below

query CodeOwnerValidation {
  project(fullPath: "flightjs/Flight") {
    repository {
    	blobs(
        ref: "code-owner-error"
      	paths: ["CODEOWNERS"]
    	) {
          nodes {
          id
          name
          validateCodeownerFile {
            total
            validationErrors {
              code
              lines
            }
          }
      	}
    	}      
    }
  }
}

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #415352 (closed) see also #216066 (comment 1445478662)