refactor - remove explicit pinning on github

[tucosaurus]

Why was this change necessary?

We explicitly pin github as the git hosting provider.

How does it address the problem?

• introduces a new variable in cookiecutter git_hosting_service.
• renames github_repository-> repository
• renames github_username -> username

Are there any side effects?

Yes. Since the generated project files were namespaced under github_repository folder, git has renamed all files. This might not be a good idea after all. Or we need to look at a more viable alternative. I am still creating this PR so that we can have a conversation around this.

[tucosaurus]

So, we can't go ahead with this since we lose all the git history.