feat: conf inherit (#2568)

* feat: add ValuerWithParent

* feat: make etcd config inherit from parents

* chore: add more tests

* chore: add more tests

* chore: add more comments

* chore: refactor

* chore: add more comments

* fix: fix duplicated code and refactor

* fix: remove unnecessary code

* fix: fix test case for removing print

* feat: support partial inherit

core/mapping/valuer_test.go

@@ -0,0 +1,33 @@
+package mapping
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMapValuerWithInherit_Value(t *testing.T) {
+	input := map[string]interface{}{
+		"discovery": map[string]interface{}{
+			"host": "localhost",
+			"port": 8080,
+		},
+		"component": map[string]interface{}{
+			"name": "test",
+		},
+	}
+	valuer := recursiveValuer{
+		current: mapValuer(input["component"].(map[string]interface{})),
+		parent: simpleValuer{
+			current: mapValuer(input),
+		},
+	}
+
+	val, ok := valuer.Value("discovery")
+	assert.True(t, ok)
+
+	m, ok := val.(map[string]interface{})
+	assert.True(t, ok)
+	assert.Equal(t, "localhost", m["host"])
+	assert.Equal(t, 8080, m["port"])
+}