Sync nodes logic

[yago-123]

Missing:

• Handle the cases in storage when element is not found (example: last header or block not added yet)
• Implement network handler and function for AskAllHeaders
• Implement serialization of block headers arrays in encoding
• Synchronization testing

[yago-123]

Add timeout options to config so the network can be debugged

[yago-123]

Next steps:

• Implement OnBlockAddition for network propagation
• Think about how to propagate a new block inserted in the chain at P2P level
• Implement mining interval correctly (difficulty variation based on time)
• Add some sort of e2e testing
• Verify that p2p-min-conn can be picked from default-config.yaml