[Feature] blockchain checkpoint

[LeoHChen]

Problem/limitation At Hand

To reduce the time to sync and size of the blockchain DB for validators or non-validating nodes.

Proposed Solution

The proposal is using a publicly published checkpoint block while the node syncs the blockchain from the checkpoint block. When a fresh new node is started, it was given an option to sync from the checkpoint block or start from the very first genesis block.

Using the checkpoint block feature can greatly reduce the number of blocks and size of data synced by the node. This is applicable to both validators and non-validating nodes.

Design discussion and engineering progress can be tracked in this issue.

Progress

https://www.notion.so/harmonyone/Blockchain-Checkpoint-1da0d61b8c644c89bbf5e2266ff859d4