Add package flagzog:

- Add FlagValidator interface
- Add BoolFlag
- Add Int64Flag
- Add StringFlag

Signed-off-by: Jan Tytgat <jan.tytgat@corelayer.eu>

flagzog/validator.go

@@ -0,0 +1,27 @@
+package flagzog
+
+import (
+	"context"
+	"log/slog"
+)
+
+type FlagValidator interface {
+	Name() string
+	Validate() ([]string, error)
+	Usage() string
+}
+
+func ValidateFlags(ctx context.Context, logger *slog.Logger, flags []FlagValidator) ([]string, error) {
+	var validatedFlags []string
+	var err error
+
+	for _, flag := range flags {
+		var issues []string
+		if issues, err = flag.Validate(); err != nil {
+			logger.Log(ctx, slog.LevelError, "validation failed", slog.String("flag", flag.Name()), slog.Any("issues", issues))
+			return validatedFlags, err
+		}
+		validatedFlags = append(validatedFlags, flag.Name())
+	}
+	return validatedFlags, nil
+}