Add support for optional drivers such as Drupal.org

[codebymikey]

Not a high priority issue, but it would be nice to have the option to easily plug in custom git drivers. e.g. Drupal.org, which handles versioning a bit differently, e.g. they have certain tag/branch prefixes such as 7-x and 8-x, (they've since switched to actual semantic versioning, but old versions will still need some basic support) and .info.yml files that need special handling to pick up composer dependencies and stuff.

Additional references for how the current https://packages.drupal.org/8/ type repos work:

• https://github.com/drupal-composer/drupal-parse-composer
• https://git.drupalcode.org/project/project_composer