config: minor changes to split config and watcher files

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

flag.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"flag"
+	"fmt"
 	"reflect"
 	"time"
 
@@ -120,6 +121,10 @@ func (c *flagConfig) Name() string {
 	return c.opts.Name
 }
 
+func (c *flagConfig) Watch(ctx context.Context, opts ...config.WatchOption) (config.Watcher, error) {
+	return nil, fmt.Errorf("not implemented")
+}
+
 func NewConfig(opts ...config.Option) config.Config {
 	options := config.NewOptions(opts...)
 	if len(options.StructTag) == 0 {