Add exempt-pr-label

We should configure [exempt-pr-label](https://github.com/actions/stale/blob/v1.1.0/action.yml#L26
) to [stale.yml](https://github.com/IBM/nodejs-itoolkit/blob/master/.github/workflows/stale.yml) to avoid closing out PRs.This has happened a few times see #179 #151.
