Fixing github webhook authorization

Adds secret to github webhooks

## Rollback Plan
* To roll back this change, revert the merge with: `git revert -m 1 MERGE_SHA` and perform another deploy.

## QA Plan
> Fill in scenarios below. Review [QA Best Practices](https://source.sportngin.com/page/show/1227795-qa-best-practices).

#### Risk Level:
- [x] Low
- [ ] Medium
- [ ] High

I'll show you it working

I believe you want this to be a class variable: `@@config ||= ...`