Support for private GitHub Enterprise installations

[satorg]

The base GitHub API URLs are hard-coded inside the GithubAPIv3Config class:

case class GithubAPIv3Config(
    baseUrl: String = "https://api.github.com/",
    authorizeUrl: String =
      "https://github.com/login/oauth/authorize?client_id=%s&redirect_uri=%s&scope=%s&state=%s",
    accessTokenUrl: String = "https://github.com/login/oauth/access_token"
)

which makes impossible to leverage github4s in those companies which use their private GitHub installations and obviously different base API URLs.

Currently it seems there's no way to override these URLs.

[satorg]

I believe I would be great to allow to override these values or/and read them from system properties and configuration files.

[BenFradet]

Definitely agreed 👍

[BenFradet]

I think we could turn that case class into an implicit parameter when instantiating Github[F](client, token)

[satorg]

Agree, I think it could look something like:

def apply[F[_]: ConcurrentEffect](
      accessToken: Option[String] = None,
      timeout: Option[Duration] = None
  )(implicit ec: ExecutionContext, config = GithubAPIv3Config.default()): Github[F]

where GithubAPIv3Config.default() creates config for the public GitHub (https://api.github.com/ etc)
although my concern here is that GithubAPIv3Config looks more like implementation details.
WDYT?

[BenFradet]

yes I think it needs renaming, maybe something like:

final case class GithubConfig(
  baseUrl: String = "https://api.github.com/",
  authorizeUrl: String = "https://github.com/login/oauth/authorize?client_id=%s&redirect_uri=%s&scope=%s&state=%s",
  accessTokenUrl: String = "https://github.com/login/oauth/access_token"
)

object GithubConfig {  
  implicit val default: GithubConfig = GithubConfig()
}

and then have:

class Github[F[_]: Sync](
    client: Client[F],
    accessToken: Option[String]
)(implicit ghConfig: GithubConfig)

👍

[satorg]

@BenFradet, I submitted a PR #384, could you take a look please?