RPC: Add get node status information

[sieniven]

Summary

• Add getnodestatusinfo RPC to get the node's health status. The RPC returns:
  • sync_to_tip flag - check whether the node's chain validation tip is fully sync-ed to the received block headers tip
  • active_peer_nodes flag - check whether the node has a minimum number of 5 connections to active peer nodes
  • health_status flag - both sync_to_tip and active_peer_nodes flags must be true for the node to be healthy status
• Expose health endpoint APIs (/livez/, /readyz) for deployment. Pass -healthendpoints to enable health endpoint APIs.
  • /livez/ - Returns status ok response once RPCs is live.
  • /readyz/ - Returns status ok response if node's chain is fully sync-ed to latest tip and has active peer nodes (based on getnodestatusinfo).

Implications

• Storage

  • Database reindex required
  • Database reindex optional
  • Database reindex not required
  • None

• Consensus

  • Network upgrade required
  • Includes backward compatible changes
  • Includes consensus workarounds
  • Includes consensus refactors
  • None