Drainpipe does not support Github enterprise

[tess-ten7]

In PantheonReviewApps.yml, the ./.github/actions/drainpipe/pantheon/review action calls out to https://api.github.com. This fails immediately on Github Enterprise instances which have a different URL. There is no way to customize the URL through a parameter either.

[deviantintegral]

This is self-hosted enterprise instances, or enterprise in the cloud? If it's the later, I bet there's some way we can automatically switch that. However, we have one client on enterprise cloud and I think we're calling api.github.com and it's wroking fine, so it's probably not needed.

For self hosted, we have no clients currently using it. I think we'd be glad to review a PR on this, but since we can't test it ourselves we'd need you or someone else with access to pick this one up.