Refactor GithubService URL handling for remote project

What

Extracts RemoteProject class to handle url manipulation

Why

If we default to using the mirroring settings for https://gitlab.com/gitlab-org/gitlab-ee/issues/5136 then we'll want to make sure we ignore the token set as the git username and remove trailing .git.

We might also want to perform validation to ensure that sub-routes like ./settings or ./pulls are not accidentally pasted by users.

We might need to handle nested hosts as mentioned in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/4591#note_61915120

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?