New static configuration loading system.

Co-authored-by: Mathieu Lonjaret <mathieu.lonjaret@gmail.com>

pkg/cli/loader_flag.go

@@ -0,0 +1,22 @@
+package cli
+
+import (
+	"fmt"
+
+	"github.com/containous/traefik/pkg/config/flag"
+	"github.com/containous/traefik/pkg/log"
+)
+
+// FlagLoader loads configuration from flags.
+type FlagLoader struct{}
+
+// Load loads the command's configuration from flag arguments.
+func (*FlagLoader) Load(args []string, cmd *Command) (bool, error) {
+	if err := flag.Decode(args, cmd.Configuration); err != nil {
+		return false, fmt.Errorf("failed to decode configuration from flags: %v", err)
+	}
+
+	log.WithoutContext().Println("Configuration loaded from flags.")
+
+	return true, nil
+}