Manage node to sync legacy blocks in the start of the node

[ishantiw]

Description

Manage node to sync legacy blocks in the start of the node (can be disabled with a flag within legacy). Disable block processing (maybe a flag on receiving a block from the network to ignore when we are syncing legacy blocks)

• In case the legacy.sync flag from the config is false then simply skip the below step
• We can call legacyChainHandler.sync and await after network.start in the engine.start so we don't have to manage sync flag and emitting event for syncing legacy blocks
• ~~Pass legacyChainHandler to consensus so that when consensus calls network.applyNodeInfo it can pass current legacy blocks~~ Since we can apply partial nodeInfo we don't have this requirement

Acceptance Criteria

• Should have unit tests covering the solution