Inject GitHub host to be able to clone from another GitHub instance (#922)

* Adding the ability to specify the GitHub Server URL and allowing for it to differ from the Actions workflow host

* Adding tests for injecting the GitHub URL

* Addressing code review comments for PR #922

src/git-source-settings.ts

@@ -83,4 +83,9 @@ export interface IGitSourceSettings {
    * Indicates whether to add repositoryPath as safe.directory in git global config
    */
   setSafeDirectory: boolean
+
+  /**
+   * User override on the GitHub Server/Host URL that hosts the repository to be cloned
+   */
+  githubServerUrl: string | undefined
 }