XDS client(Local) used to sync the databases

[nickolaev]

Summary

When Local CP receives a new set of Kuma resources, it should sync it with Local storage.

Process of syncing:

1. Retrieve all policies from Local CP storage
2. Remove all that are not in received set
3. Add all that are in received set but not in Local CP
4. Compare the existing one by their spec and update if needed.

Do not sync ingress from the same cluster as your local CP

The simpler implementation would be to wipe out all resources from Local CP and replace them with set of received resources. This however has two disadvantages:

• more I/O operation on Local Storage
• you need to lock the XDS/SDS reconciliation loop for this process.