Allow Personal Access Token for GitHub repo webhook

[Scott-Wallace-ConnectedLab]

Instead of forcing a username/password when setting up the GitHub webhook, allow for the use a GitHub Personal Access Token instead.

[geekflyer]

you can use personal access tokens as password actually.

[drewwells]

I tried this with SSO enabled personal access token, and see the following error:

"finished unary call with code PermissionDenied" error="rpc error: code = PermissionDenied desc = permission denied: repositories, create, https://github.com/...therepo..." grpc.code=PermissionDenied grpc.method=Create grpc.service=repository.RepositoryService grpc.start_time="2019-07-25T12:36:19Z" grpc.time_ms=0.539 span.kind=server system=grpc