github: Add get_repository_metadata method to GitHubSession class
It returns the full JSON metadata of a GitHub repository by querying the GitHub REST API.
Also refactor get_canonical_url method with it.
Related to swh-loader-git#3652.
Staging instance, all changes can be removed at any time
It returns the full JSON metadata of a GitHub repository by querying the GitHub REST API.
Also refactor get_canonical_url method with it.
Related to swh-loader-git#3652.