[StructUtil] add support that the Struct can nest any type to transform (#80)

* add support json tag attribute for StructToMap function

* add the structutil to provide more rich functions and fixed #77

* add support that the nested struct to map for structutil

* recover code

* add structutil unit test

* [StructUtil] add unit test

structutil/error.go

@@ -0,0 +1,7 @@
+package structutil
+
+import "fmt"
+
+func ErrInvalidStruct(v any) error {
+	return fmt.Errorf("invalid struct %v", v)
+}