State Sync V2

[JoshLind]

This issue is to track the development of the DIP for state sync v2. A pull request with a draft DIP will follow shortly. The TL;DR for those interested:

• Problem: State sync v1.1 [1] only offers a single primitive strategy for keeping nodes up-to-date. This strategy is slow (i.e., it requires syncing and executing all transactions from genesis), expensive (i.e., it requires downloading, executing and storing the entire transaction history), inflexible (i.e., it is unable to adapt to different use-cases and requirements) and brittle (i.e., the implementation tightly couples Diem components and Diem nodes).
• Solution: We propose a new state sync framework (state sync v2) that supports multiple state sync strategies based on use-cases. The strategies trade-off security, performance and resources. Strategies include: syncing from genesis, syncing directly from a waypoint and syncing without executing. The new framework decouples intra-node components (e.g., state sync and storage) and removes coupling between Diem nodes (e.g., allowing additional strategies to be introduced without breaking backward compatibility).

[1] diem/diem#6795