Private repos aren't accessible by the webhook

[danhalson]

The raspberrypigithubbot does not have visibility of private repos, and as a result attempts to build from these will fail. Previously this has been worked around by manually giving the bot permission, and ensuring the project is not shared on learning admin, however this is brittle and requires manually changing.

Some investigation is needed but it may be this restriction just isn't necessary, and as long as it's not visible on learning admin, no harm will be done.

[create-issue-branch]

Branch feature/505-Private_repos_aren_t_accessible_by_the_webhook created!

[danhalson]

The raspberrypigithubbot user has now been given owner permissions so it can see and manage all repos (private and public) - however, the api key is still scoped so as to limit capabilities to reading repos.