log: Replace ctxlogrus (pt.1)

This MR is the first part towards replacing the ctxlogrus package, which is going away with go-grpc-middleware v2. Instead, we're introducing a new set of context-aware logging facilities DebugContext() and similar that are able to extract information from the context itself. These new facilities match the interface that the slog package provides and are thus a natural step into the direction of eventually adopting slog as our logging backend.