pkg/reloader: Provide option to use slog instead of go-kit

[ArthurSens]

Slog was added to the Go standard libraries as an alternative for structured logging. A lot of tools are trying to migrate to slog, aiming to remove their dependency tree in third-party libraries like go-kit

• Replace github.com/go-kit/klog by the new slog package prometheus-operator/prometheus-operator#6183

The reloader package still requires go-kit in its constructor:

thanos/pkg/reloader/reloader.go

Line 75 in 8d3d34b

"github.com/go-kit/log"

thanos/pkg/reloader/reloader.go

Line 186 in 8d3d34b

func New(logger log.Logger, reg prometheus.Registerer, o *Options) *Reloader {

Would it make sense to provide another one with slog?