beta site: set up github webhooks for debugging

[jenlampton]

(todo: create this ticket)

[docwilmot]

https://forum.backdropcms.org/comment/3825#comment-3825
This issue was created as a response to the forum post above. We noticed that there were several errors in the backdrop CMS logs and we are trying to find ways to solve this problem.

But I think I might have a better idea than either a test site or using NGROK. And that is I'm going to try a PR to GitHubAPI module to enable test webhooks.

[bugfolder]

During the dev meeting, @quicksketch mentioned that he'd found a way to simulate webhooks on his local system by (IIRC) looking in the Github log to get what was sent in a past webhook, then using curl locally to send that to his local dev system. That sounded pretty slick, and I think he was planning on documenting somewhere. (Or re-documenting, since it was suggested at the meeting that it might have been described in a past issue.)