Support GitHub hooks that check pull-request authors against CLA signatories and employees

Provide a mechanism at JBoss.org by which a GitHub project/organization can create a “pull_request” hook that automatically checks whether the author of the pull-request has signed a JBoss CLA or is a current Red Hat employee. For example, this hook might add a comment to the pull request that says "CLA found" or “CLA not found" or even "CLA pending".

Note that we may need to verify with the legal team whether we can publicize this information, and that such a publicly-available service is acceptable and cannot be abused.

Also, there would need to be a way to re-evaluate the PR, for example after the author submitted a CLA.

Automating the verification of a signed CLA will help ensure that projects do not inadvertently merge changes submitted by those that have not (yet) signed a CLA.