Allow permissions for public repositories only

[KLBa]

Before connecting to GitHub, CircleCI allows to select whether the user wants to give permission to access private repositories or not.

It would be nice to have this feature for the ADR-Manager as well, especially because we aren't security experts.

As a: User I want to: be able to select to only allow access to public repositories so that: I can only edit public repositories but keep private ones private.