Prevent release if codeowners is not valid

As discussed with language leads: we need to prevent release and allow teams to unblock themselves.

The plan for this is to build tooling which validates that a package being released has the correct number of CODEOWNERS. This is done by reading the data model and figuring out if the number of owners is valid.

In addition to this it was also discussed with @ronniegeraghty that we need to validate that a package has PR labels associated with it and that the labels themselves have service owners in the repo.