github and gitea: Use html_url as @id and clone_url as codeRepository

They are closer semantics as 'html_url' is the main page of the repository, so it is the best to identify it; and 'clone_url' is the URL that should be given to 'git clone', as documented by https://schema.org/codeRepository

Additionally, that property was missing so far; but a future commit will need to use it to identify fork relationships (node ids are required to representation relationships between documents as we cannot use blank nodes for that)

Depends on !391 (closed).

Migrated from D8468 (view on Phabricator)