Deep copy does not copy fields in the specified structure

[robotLJW]

Deep copy does not copy fields in the specified structure

In some scenarios, it is not necessary to copy all the fields.

Motivation

In the cache, data is stored with pointers. Now there is a scenario where only some fields of this data need to be removed, but the pointer content cannot be modified. Due to the complexity of data structure, only deep copy can be used.

Related Issues

https://github.com/apache/servicecomb-service-center/pull/921