feat(lib/logging): add slog filter handler, move slog init logic here

Signed-off-by: Xe Iaso <me@xeiaso.net>

lib/logging/logging.go

@@ -0,0 +1,24 @@
+package logging
+
+import (
+	"fmt"
+	"log/slog"
+	"os"
+)
+
+func Init(level string) slog.Handler {
+	var programLevel slog.Level
+	if err := (&programLevel).UnmarshalText([]byte(level)); err != nil {
+		fmt.Fprintf(os.Stderr, "invalid log level %s: %v, using info\n", level, err)
+		programLevel = slog.LevelInfo
+	}
+
+	leveler := &slog.LevelVar{}
+	leveler.Set(programLevel)
+
+	h := slog.NewJSONHandler(os.Stderr, &slog.HandlerOptions{
+		AddSource: true,
+		Level:     leveler,
+	})
+	return h
+}