feat: initial shared logging module

slog SetupLogger (text/json/otel), context logger helpers, MockLogger test
helper, and a request-logger HTTP middleware sub-package. Replaces the logging
package + middleware request-logger copied across the backend services.

log.go

@@ -0,0 +1,63 @@
+package logging
+
+import (
+	"context"
+	"log/slog"
+	"os"
+
+	"go.opentelemetry.io/contrib/bridges/otelslog"
+)
+
+type Logger interface {
+	Info(msg string, args ...any)
+	Warn(msg string, args ...any)
+	Error(msg string, args ...any)
+}
+
+var defaultLogger *slog.Logger
+
+type contextKey string
+
+const loggerKey = contextKey("logger")
+
+func SetupLogger(logLevel, logFormat, serviceName, buildVersion string) *slog.Logger {
+	var leveler slog.LevelVar
+
+	err := leveler.UnmarshalText([]byte(logLevel))
+	handlerOpts := &slog.HandlerOptions{
+		AddSource:   false,
+		Level:       leveler.Level(),
+		ReplaceAttr: nil,
+	}
+	var handler slog.Handler
+	switch logFormat {
+	case "json":
+		handler = slog.NewJSONHandler(os.Stdout, handlerOpts)
+	case "text":
+		handler = slog.NewTextHandler(os.Stdout, handlerOpts)
+	case "otel":
+		handler = otelslog.NewHandler(serviceName,
+			otelslog.WithVersion(buildVersion))
+	}
+	defaultLogger = slog.New(handler).With("service", serviceName).With("version", buildVersion)
+	if err != nil {
+		defaultLogger.With("err", err).Error("Failed to parse log level")
+		os.Exit(1)
+	}
+	slog.SetDefault(defaultLogger)
+	return defaultLogger
+}
+
+// ContextWithLogger returns a new Context with the logger attached
+func ContextWithLogger(ctx context.Context, logger *slog.Logger) context.Context {
+	return context.WithValue(ctx, loggerKey, logger)
+}
+
+// LoggerFromContext returns a logger from the passed context or the default logger
+func LoggerFromContext(ctx context.Context) *slog.Logger {
+	logger := ctx.Value(loggerKey)
+	if l, ok := logger.(*slog.Logger); ok {
+		return l
+	}
+	return defaultLogger
+}