ODK seed command should have an option for setting up a repo on gitlab

See comments by @leechuck on twitter: https://twitter.com/leechuck2/status/1156588240817856512

Developers of certain nationalities/countries may not be able to use GitHub.

Currently when seeding a repo, there are certain assumptions made the repo will be deposited on GH. It's not hard for an expert to figure out how to adapt this to GL or anywhere else, but we should make this easier for people.

Note: this doesn't address the fact that the wider ecosystem we are developing is very GH-centric

Start from the ODK seed command and inspect where repository setup assumes GitHub. Trace the related GitHub references and determine the option and setup behavior needed for GitLab; done means a repository can be seeded on GitLab without relying on GitHub assumptions.

Written by the indexing model from the issue text.