Missing support for deployment environments

[charlie-collard]

Deployment environments are missing from the library. For example, I can't get, list, create, update, or delete deployment environments.

GitHub REST API documentation for deployment environments

Note: Deployment environments may be indirectly created via creating a deployment and specifying a string in the environment field:

import org.kohsuke.github.GitHub

private void createDeployment() {
    GitHub.connectUsingOAuth("githubToken")
        .getRepository("user/repo")
        .createDeployment("1.0")
        .environment("production")
        .create()
}

[rpeb]

Hi @bitwiseman I want to work on this issue.