Feature request: Better debug-ability for events from GitHub

[nolessafool]

When something goes "wrong" with git-gateway, the logs shown are not super useful in debugging some problems like this:

[When using Git Gateway] ... the logs don't show if Github is sending us an HTTP 500 or another type of error, or why Netlify might be generating 500 errors. I wish we passed the error string in to the logs!

- What is the current behavior?

Current behavior is hard to debug :)

- Please mention your Go version, and operating system version.

This is the netlify-hosted instance of git-gateway as impacting our ability to help a paying customer in this case: https://app.intercom.io/a/apps/q245f50x/inbox/inbox/1479299/conversations/20976185270

[HeyITGuyFixIt]

This is still something that would be useful. I am dealing with HTTP 500 errors with no explanation and no way to debug. I am essentially shooting in the dark here. I am working with GitLab.