Use authenticated client to interact with github API

[90lantran]

Right now, the server uses un-authenticated client which only has limit 60 requests/hour. If authenticated, we can request up to 5000 requests/hour.
The go-github library does provide authentication with it. However, there are some reported issues for JWT google/go-github#1069.
Another way is to use the personal access token which is straight forward but cannot be used for production.
One last way is to authentication as github app which requires a call back URL which is where the server which be hosted. Localhost will not be accepted for a callback URL.