Dinghy Crashing for Customers using 2.24+ when customers are using a Custom Endpoint

Issue

Customers using a Custom Endpoint are seeing crashes occur using 2.24+.  Upon observing the Dinghy logs, there is a notification that the service is attempting to reach out to api.github.com instead of the set custom endpoint.   Below is an example of such an error 2021/05/09 04:51:01 POST https://api.github.com/repos/armory-test/dinghy-test/commits/9999xx999x9xx9xxx9xx99x99x99xx99x9x99xx9/comments: 401 Bad credentials []

Cause

As of 2.24.x, a change was made to push comments on Dinghy outputs back into the comment of the PR.  This is a part of the notifications setting that was added to Dinghy to allow for more robust and detailed information about the results from a PR commit.  Currently, the notification only supports using Github Cloud, using the api.github.com endpoint, and does not account for custom endpoints