Remove dependency to gh package

[ahasverus]

Feature description

This idea here is to remove the dependency to the gh package. This will reduce the number of packages to depend on and make easier the tests.

This implies to deeply refactor:

• functions that query the GitHub API by using the httr2 package (already started here)
• gh::gh_token() by using directly the gitcreds package

Some helpers will be needed:

• stop_if_gh_account_missing(meta)
• stop_if_gh_org_does_missing(organisation)
• stop_if_gh_repo_missing(meta)
• stop_if_gh_token_missing()

Also update_gh_repo() needs to be deeply refactored.