add before Init func support

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

vault_test.go

@@ -0,0 +1,23 @@
+package vault
+
+import (
+	"context"
+	"testing"
+
+	"go.unistack.org/micro/v3/codec"
+	"go.unistack.org/micro/v3/config"
+)
+
+func TestInit(t *testing.T) {
+	c := NewConfig(
+		config.Context(context.TODO()),
+		config.Codec(codec.NewCodec()),
+		config.BeforeInit(func(ctx context.Context, c config.Config) error {
+			return c.Init(Token("tkn"), config.BeforeInit(nil))
+		}),
+	)
+
+	if err := c.Init(); err != nil {
+		t.Fatal(err)
+	}
+}