Add Github Enterprise support

[zapplebee]

Allows for environmental variables to be configured to access GitHub Enterprise

export GITHUB_DOMAIN=git.{YOURDOMAIN}.com
export GITHUB_PERSONAL_ACCESS_TOKEN={a personal access token with the correct permissions to read users}
export GITHUB_COOKIE={a cookie copied from an active browser session (this should work with pretty much all SSO implementations}
npm run start

[kateefimova-eb]

Wouldn't it be easier to implement it similarly to how the code currently reads GitHub's html? Considering that there are GitLab graphs, that is. I could also be wrong considering I'm not too familiar with GitLab myself!

[zapplebee]

There are really only two differences between GitHub and GitHub Enterprise (GHE)

1. The API is at a different URL.
2. The user is logged in, usually via some kind of federated model (SSO)

In order to not implement the login flow, two-factor, etc, the easiest solution is to just expect the user to copy an active token from a browser session.

Other than changing the URLs and setting additional headers, this solution uses the same parser solution.

[kateefimova-eb]

Just tried to access the GitLab url with a random existing username and you were right, it did ask me to login.

Thank you for your time and effort to create this PR, I will review it closer after work! 👏