Introduce a wrapper for the logrus logging infrastructure. This is a
first step towards abstracting away the actual implementation of our
logs behind a type that we can iterate on and will thus pave the way
towards adoption of the `slog` package.

Note that this is only one step of this transition. The interface does
not yet roundtrip to itself, e.g. calling `log.Logger.WithError()` will
result in a `logrus.Entry`, not in a `log.Logger`. This will be handled
at a later point.